6%2D4 Elimination Using · PDF fileThe solution is (2, ±4). 8x + 3y = í7 ... So,...

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Use elimination to solve each system of equations. 2x í y = 4 7x + 3 y = 27 62/87,21 Notice that if you multiply the first equation by 3, the coefficients of the y ±terms are additive inverses. Now, substitute 3 for x in either equation to find y . The solution is (3, 2). 2x + 7 y = 1 x + 5 y = 2 62/87,21 Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses. Now, substitute 1 for y in either equation to find x. The solution is (±3, 1). eSolutions Manual - Powered by Cognero Page 1 6 - 4 Elimination Using Multiplication

Transcript of 6%2D4 Elimination Using · PDF fileThe solution is (2, ±4). 8x + 3y = í7 ... So,...

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 1

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 2

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 3

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 4

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 5

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 6

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 7

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 8

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 9

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 10

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 11

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 12

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 13

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 14

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 15

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 16

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 17

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 18

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 19

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 20

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 21

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 22

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 23

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 24

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 25

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 26

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 27

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 28

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 29

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 30

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 31

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 32

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 33

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 34

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 35

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 36

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

eSolutions Manual - Powered by Cognero Page 37

6-4 Elimination Using Multiplication

Use elimination to solve each system of equations.���2x í y = 4

7x + 3y = 27

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

� The solution is (3, 2).

���2x + 7y = 1 x + 5y = 2

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (±3, 1).

���4x + 2y = í14 5x + 3y = í17

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by ±2, the coefficients of the y±terms are additive inverses. �

� Now, substitute ±4 for x in either equation to find y . �

� The solution is (±4, 1).

���9a í 2b = í8 í7a + 3b = 12

62/87,21���Notice that if you multiply the first equation by 3 and the second equation by 2, the coefficients of the y±terms are additive inverses. �

� Now, substitute 0 for a in either equation to find b. �

� The solution is (0, 4).

���.$<$.,1*� A kayaking group with a guide travels 16 miles downstream, stops for a meal, and then travels 16 miles upstream. The speed of the current remains constant throughout the trip. Find the speed of the kayak in still water.

62/87,21���Let x represent the speed of the kayak and y represent the speed of river. � The rate to travel down river would be with the current so the speed of kayak and speed of river are added. The UDWH�WR�WUDYHO�DJDLQVW�WKH�FXUUHQW�ZRXOG�EH�WKH�GLIIHUHQFH�EHWZHHQ�WKH�VSHHG�RI�WKH�ND\DN�DQG�VSHHG�RI�WKH�ULYHU��

Notice that the coefficients of the y±terms are additive inverses, so add the equations. �

� So, the speed of the kayak is 6 mph.

� speed of kayak

speed ofriver

time (hours) d d = rt

ZLWK� current x y 2 16 16 = 2(x + y)

DJDLQVW�current x y 4 16 16 = 4(x + y)

���32'&$676� Steve subscribed to 10 podcasts for a total of 340 minutes. He used his two favorite tags, Hobbies and Recreation and Soliloquies. Each of the Hobbies and Recreation episodes lasted about 32 minutes. Each Soliloquies episodes lasted 42 minutes. To how many of each tag did Steve subscribe?

62/87,21���Let x represent the number of Hobbies and Recreation podcasts and y represent the number of Soliloquies podcasts. Since Steve subscribed to 10 podcasts, then the number of Hobbies and Recreation and number of Soliloquies would equal 10. Each Hobbies and Recreation podcast talks 32 minutes. SO the total minutes for Hobbies and Recreation podcast is 32x. Each Soliloquies podcast talks 42 minutes. So the total minutes for Soliloquies podcast is 42x. Add WKHVH�DQG�HTXDO�WR�WKH�WRWDO�PLQXWHV�RI������ �

� Notice that if you multiply the first equation by ±32, the coefficients of the x±terms are additive inverses. �

� Now, substitute 2 for y in either equation to find x. �

� Steve subscribed to 2 Soliloquies and 8 Hobby and Recreation podcasts.

Use elimination to solve each system of equations.���x + y = 2 í3x + 4y = 15

62/87,21���Notice that if you multiply the first equation by 3, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±1, 3).

���x í y = í8 7x + 5y = 16

62/87,21���Notice that if you multiply the first equation by 5, the coefficients of the y±terms are additive inverses.�

� Now, substitute ±2 for x in either equation to find y . �

� The solution is (±2, 6).

���x + 5y = 17 í4x + 3y = 24

62/87,21���Notice that if you multiply the first equation by 4, the coefficients of the x±terms are additive inverses.�

� Now, substitute 4 for y in either equation to find x. �

� The solution is (±3, 4).

����6x + y = í39 3x + 2y = í15

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the y terms are additive inverses.�

� Now, substitute ±7 for x in either equation to find y . �

� The solution is (±7, 3).

����2x + 5y = 11 4x + 3y = 1

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 3 for y in either equation to find x. �

� The solution is (±2, 3).

����3x í 3y = í6 í5x + 6y = 12

62/87,21���Notice that if you multiply the first equation by 2, the coefficients of the y±terms are additive inverses.�

� Now, substitute 0 for x in either equation to find y. �

� The solution is (0, 2).

����3x + 4y = 29 6x + 5y = 43

62/87,21���Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 5 for y in either equation to find x. �

� The solution is (3, 5).

����8x + 3y = 4 í7x + 5y = í34

62/87,21���Notice that if you multiply the first equation by 7 and the second equation by 8, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±4 for y in either equation to find x. �

� The solution is (2, ±4).

����8x + 3y = í7 7x + 2y = í3

62/87,21���Notice that if you multiply the first equation by ±2 and the second equation by 3, the coefficients of the y±terms are additive inverses. �

� Now, substitute 1 for x in either equation to find y . �

� The solution is (1, ±5).

����4x + 7y = í80 3x + 5y = í58

62/87,21���Notice that if you multiply the first equation by ±3 and the second equation by 4, the coefficients of the x±terms are additive inverses. �

� Now, substitute ±8 for y in either equation to find x. �

� The solution is (±6, ±8).

����12x í 3y = í3 6x + y = 1

62/87,21���Notice that if you multiply the second equation by ±2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� The solution is (0, 1).

����í4x + 2y = 0 10x + 3y = 8

62/87,21���Notice that if you multiply the first equation by ±3 and multiply the second equation by 2, the coefficients of the y±terms are additive inverses. �

Now, substitute �IRU�x in either equation to find y .

The solution is .

����180%(5�7+(25<� Seven times a number plus three times another number equals negative one. The sum of thetwo numbers is negative three. What are the numbers?

62/87,21���Let x represent one number and y represent the second number. �

� Notice that if you multiply the second equation by ±3, the coefficients of the y±terms are additive inverses.�

� Now, substitute 2 for x in either equation to find y . �

� So, the two numbers are 2 and ±5.

����)227%$//� A field goal is 3 points and the extra point after a touchdown is 1 point. In a recent post±season, Adam Vinatieri of the Indianapolis Colts made a total of 21 field goals and extra point kicks for 49 points. Find the number of field goals and extra points that he made.

62/87,21���Let x represent the number of field goals and y represent the number of extra point kicks. �

� Notice that if you multiply the first equation by ±1, the coefficients of the y±terms are additive inverses.�

� Now, substitute 14 for x in either equation to find y . �

� So, he made 14 field goals and 7 extra point kicks.

Use elimination to solve each system of equations.����2.2x + 3y = 15.25

4.6x + 2.1y = 18.325

62/87,21���Notice that if you multiply the first equation by ±2.1 and the second equation by 3, the coefficients of the y±terms areadditive inverses. �

� Now, substitute 2.5 for x in either equation to find y . �

� So, the solution is (2.5, 3.25).

����í0.4x + 0.25y = í2.175 2x + y = 7.5

62/87,21���Notice that if you multiply the second equation by ±0.25, the coefficients of the y±terms are additive inverses.�

� Now, substitute 4.5 for x in either equation to find y . �

� So, the solution is (4.5, ±1.5).

����

62/87,21���Notice that if you multiply the second equation by ±8, the coefficients of the y±terms are additive inverses.�

� Now, substitute 3 for x in either equation to find y . �

So, the solution is .

����

62/87,21���Notice that if you multiply the second equation by ±12, the coefficients of the y±terms are additive inverses.�

Now, substitute �IRU�x in either equation to find y .

� So, the solution is .

����CCSS MODELING �$�VWDIILQJ�DJHQF\�IRU�LQ-home nurses and support staff places necessary personal at locationson a daily basis. Each nurse placed works 240 minutes per day at a daily rate of $90. Each support staff employee works 360 minutes per day at a daily rate of $120. � a. On a given day, 3000 total minutes are worked by the nurses and support staff that were placed. Write an HTXDWLRQ�WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � b. On the same day, $1050 of total wages were earned by the placed nurses and support staff. Write an equation WKDW�UHSUHVHQWV�WKLV�UHODWLRQVKLS�� � F���Solve the system of equations, and interpret the solution in context of the situation.

62/87,21���D�� Let n represent the number of nurse¶s minutes and s represent the number of support staff minutes. 240n + 360s = 3000 � E�� 90n + 120s = 1050 � F�� Notice that if you multiply the second equation by ±3, the coefficients of the s±terms are additive inverses. �

� Now, substitute 5 for n in either equation to find s. �

��������

����*(20(75<� The graphs of x + 2y = 6 and 2x + y = 9 contain two of the sides of a triangle. A vertex of the triangle is at the intersection of the graphs. � D�� What are the coordinates of the vertex? � E�� Draw the graph of the two lines. Identify the vertex of the triangle. � F�� The line that forms the third side of the triangle is the line x í y = í3. Draw this line on the previous graph. � G�� Name the other two vertices of the triangle.

62/87,21���D�� Notice that if you multiply the first equation by ±2, the coefficients of the x±terms are additive inverses. �

� Now, substitute 1 for y in either equation to find x. �

� The vertex is (4, 1). � b. Rewrite each equation in slope-intercept form and then graph on the same coordinate plane. �

The vertex is (4, 1). � c. Rewrite the equation in slope-intercept form and then graph the line on the same coordinate plane with the first two equations.

� G�� To find the other two vertices, use elimination to find the solutions to the other two systems of equations created by the three lines. �

� Substitute 3 for y in either equation to find the value of x.

� So, the vertex is (0, 3).

� Substitute 2 for x in either equation to find the value of y .

� So, the vertex is (2, 5).

����(17(57$,10(17� At an entertainment center, two groups of people bought batting tokens and miniature golf games, as shown in the table. �

� D�� Define the variables, and write a system of linear equations from this situation. � E�� Solve the system of equations, and explain what the solution represents.

62/87,21���D�� Let x = the cost of a batting token and let y = the cost of a miniature golf game; 16x + 3y = 30 and 22x + 5y = 43.� b. Notice that if you multiply the first equation by ±5 and the multiply the second equation by 3, the coefficients of the y±terms are additive inverses. �

Now, substitute 1.5 for x in either equation to find y . �

� The solution is (1.5, 2). A batting token costs $1.50 and a game of miniature golf costs $2.00.

����7(676� Mrs. Henderson discovered that she had accidentally reversed the digits of a test score and did not give a student 36 points. Mrs. Henderson told the student that the sum of the digits was 14 and agreed to give the student his correct score plus extra credit if he could determine his actual score. What was his correct score?

62/87,21���Let x represent the tens digit and y represent the ones digit. � The sum of the digits is 14, so x + y = 14. Since Mrs. Henderson switched the digits, she gave the students 10y + x points, when they actually earned 10x + y �SRLQWV�7KH�GLIIHUHQFH�LQ�SRLQWV�RZHG�DQG�SRLQWV�JLYHQ�LV����� �

� Notice that if you multiply the first equation by 9 the x±terms are the same, so subtract the equations. �

Now, substitute 5 for y in either equation to find x. �

� So, the correct score is 95.

����5($621,1*� Explain how you could recognize a system of linear equations with infinitely many solutions.

62/87,21���The system of equations 2x - 5y = 14 and 12x - 30y = 84 will have infinitely many solutions. You can solve by substitution or elimination and get a true statement, such as, 0 = 0. You can also notice that 12x - 30y = 84 is 6(2x - 5y = 14). The system of equations will have infinitely many solutions whenever one of the equations is a multiple of the other.

����(5525�$1$/<6,6� Jason and Daniela are solving a system of equations. Is either of them correct? Explain yourreasoning.

� �

62/87,21���Jason is correct. In order to eliminate the r±terms, you must multiply the second equation by 2 and then subtract, or multiply the equation by í2 and then add. When Daniela subtracted the equations, she should have gotten r + 16t = 18, instead of r = 18. The t-term should not be eliminated. She needs to find multiples of the equations that have the VDPH�FRHIILFLHQW�RU�RSSRVLWH�FRHIILFLHQWV�IRU�HLWKHU�r or t before adding or subtracting the equations.

����23(1�(1'('� Write a system of equations that can be solved by multiplying one equation by í3 and then adding the two equations together.

62/87,21���Sample answer: 2x + 3y = 6, 4x + 9y = 5 �

� Substitute for x in either equation and solve for y . �

����&+$//(1*(� The solution of the system 4x + 5y = 2 and 6x í 2y = b is (3, a). Find the values of a and b. Discuss the steps that you used.

62/87,21���We already know that the value of x is 3. We can use that to find y . Substitute 3 for x and solve for y . �

� So y = ±2, which means that a = ±2. Now substitute ±2 for y and 3 for x into the second equations and solve for b.�

� a = í2, b = 22

����WRITING IN MATH Why is substitution sometimes more helpful than elimination, and vice versa?

62/87,21���Sample answer: It is more helpful to use substitution when one of the variables has a coefficient of 1 or if a coefficient can be reduced to 1 without turning other coefficients into fractions. Otherwise, elimination is more helpful because it will avoid the use of fractions when solving the system.

����What is the solution of this system of equations?

$� (3, 3) %� (í3, 3) &� (í3, 1) '� (1, í3)

62/87,21���Notice that if you multiply the second equation by 2, the coefficients of the x±terms are additive inverses.�

� Now, substitute 1 for y in either equation to find x. �

� So, the solution is (±3, 1) and the correct choice is C.

����A buffet has one price for adults and another for children. The Taylor family has two adults and three children, and their bill was $40.50. The Wong family has three adults and one child. Their bill was $38. Which system of equationscould be used to determine the price for an adult and for a child?

62/87,21���If x is the adult ticket price and y is the child¶s ticket price, then the Taylor family¶s price would be 2 adults (2x) and 3 children (3y). That means that their price could be represented by . Thus, you can eliminate choices F and J. The Wong family has 3 adults (3x) and 1 child (1y), so their price could be represented by

. Therefore, the correct choice is G.

����6+257�5(63216(� A customer at a paint store has ordered 3 gallons of ivy green paint. Melissa mixes the paintin a ratio of 3 parts blue to one part yellow. How many quarts of blue paint does she use?

62/87,21���Let b represent the number of quarts of blue paint mixed and y represent the number of quarts of yellow paint PL[HG���,I�WKH�FXVWRPHU�RUGHUHG���JDOORQV�RI��SDLQW��0HOLVVD�QHHGV�WR�PL[�������RU����TXDUWV��:ULWH�D�V\VWHP�RI�equations that describes the problem. first equation:�����E + y = 12

VHFRQG�HTXDWLRQ���� If the first equation is solved for y , you get y = 12 - b. Substitute this into the second equation and solve for b. �

Therefore, she will need 9 quarts of blue paint.

����352%$%,/,7<� The table shows the results of a number cube being rolled. What is the experimental probability of rolling a 3? �

$��

%��

� &� 0.2 � '� 0.1

Outcome Frequency 1 4 2 8 3 2 4 0 5 5 6 1

62/87,21���Find the total number of outcomes = 4 + 8 + 2 + 5 + 1 = 20.

The experimental probability is .

� So, the correct choice is D.

Use elimination to solve each system of equations.����f + g = í3

f í g = 1

62/87,21���Notice the coefficients for the g±terms are the opposite, so add the equations.�

� Now, substitute ±1 for f in either equation to find g. �

� The solution is (±1, ±2).

����6g + h = í7 6g + 3h = í9

62/87,21���Notice the coefficients for the g±terms are the same, multiply equation 2 by ±1, then add the equations to find h.�

� Now, substitute ±1 for h in either equation to find g. �

� The solution is (±1, ±1).

����5j + 3k = í9 3j + 3k = í3

62/87,21���Notice the coefficients for the k±terms are the same, multiply equation 2 by ±1 and add the equations to find j .�

� Now, substitute ±3 for j in either equation to find k . �

� The solution is (±3, 2).

����2x í 4z = 6 x í 4z = í3

62/87,21���Notice the coefficients for the z±terms are the same, so multiply equation 2 by ±1 and add the equations to find x.�

� Now, substitute 9 for x in either equation to find z . �

� The solution is (9, 3).

����í5c í 3v = 9 5c + 2v = í6

62/87,21���Notice the coefficients for the c±terms are the opposite, so add the equations.�

� Now, substitute ±3 for v in either equation to find c. �

� The solution is (0, ±3).

����4b í 6n = í36 3b í 6n = í36

62/87,21���Notice the coefficients for the n±terms are the same, so multiply equation 2 by ±1 and add the equations to find b.�

� Now, substitute 0 for b in either equation to find n. �

� The solution is (0, 6).

����-2%6� Brandy and Adriana work at an after±school child care center. Together they cared for 32 children this week. Brandy cared for 0.6 times as many children as Adriana. How many children did each girl care for?

62/87,21���Let b represent the number kids Brandy watched and a represent the number of kids Adriana watched.b + a = 32 b = 0.6a Substitute 0.6a for b in the first equation to find the value of a. �

� Now, substitute 20 for a in either equation to find b. �

� So, Brandy cared for 12 children and Adriana cared for 20 children.

Solve each inequality. Then graph the solution set.����|m í 5| ��

62/87,21���

The solution set is {m|m ����DQG�m �í3}. To graph the solution set, graph m ����and graph m �í3. Then find the intersection.

and

����|q + 11| < 5

62/87,21���

The solution set is {q|q < í6 and q > í16}. To graph the solution set, graph q < í6 and graph q > í16. Then find the intersection.

and

����|2w + 9| > 11

62/87,21���

The solution set is {w|w > 1 or w < í10}. Notice that the graphs do not intersect. To graph the solution set, graph w > 1 and graph w < í10. Then find the union.

or

����|2r + 1| ��

62/87,21���

The solution set is {r|r ���or r í5}. Notice that the graphs do not intersect. To graph the solution set, graph r ���and graph r í5. Then find the union.

or

Translate each sentence into a formula.����The area A of a triangle equals one half times the base b times the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area A of a triangle equals one±half times the base b times the height h.

A equals times b times h

A = � b � h

����The circumference C of a circle equals the product of 2, ʌ, and the radius r.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The circumference C of a circle equals the product of 2, ʌ�, and the radius r.

C equals 2 times ʌ times r C = 2 � ʌ � r

����The volume V of a rectangular box is the length �times the width w multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a rectangular box is the length �WLPHV�the width w multiplied by the height h.

V equals times w times h V = � w � h

����The volume of a cylinder V is the same as the product of ʌ�and the radius r to the second power multiplied by the height h.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The volume V of a cylinder is the same as the product of ʌand the radius r to the second power multiplied by the height h.

V equals ʌ times r squared times h V = ʌ � r 2 � h

����The area of a circle A equals the product of ʌ and the radius r squared.

62/87,21���Rewrite the verbal sentence so it is easier to translate. The area of a circle A equals the product of ʌ�and the radius r squared.

A equals ʌ times r squared A = ʌ � r 2

����Acceleration A equals the increase in speed s divided by time t in seconds.

62/87,21���Rewrite the verbal sentence so it is easier to translate. Acceleration A equals speed s divided by time t in seconds.

A equals s divided by t A = s · t

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6-4 Elimination Using Multiplication