6th Grade Math: 1-4 HW

Course 1

1-5 Mental Math

6th Grade Math: 1-5 HW

Page 26

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1-5 Mental Math

Course 1

Warm UpWarm Up

Lesson PresentationLesson Presentation

Problem of the DayProblem of the Day

Warm UpFind each sum or product.

1. 17 + 15

2. 29 + 39

3. 8(24)

4. 7(12)

5. 3(91)

6. 6(15)

32

68

192

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1-5 Mental Math

84273

90

Problem of the Day

Determine the secret number from the following clues:• The number is a multiple of 5.• It is divisible by 3.• It is less than 200.• Its tens digit equals the sum of its other two digits.165

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1-5 Mental Math

Today’s Learning Goal

Learn to use number properties to compute mentally.

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1-5 Mental Math

Vocabulary

Commutative PropertyAssociative PropertyDistributive Property

Insert Lesson Title Here

Course 1

1-5 Mental Math

Course 1

1-5 Mental Math

Mental math means “doing math in your head.”

Course 1

1-5 Mental Math

COMMUTATIVE PROPERTY (Ordering)

Words Numbers

You can add or multiply numbers in any order.

18 + 9 = 9 + 1815 2 = 2 15

Course 1

1-5 Mental Math

ASSOCIATIVE PROPERTY (Grouping)

Words NumbersWhen you are only adding or only multiplying, you can group any of the numbers together.

(17 + 2) + 9 = 17 + (2 + 9) (12 2) 4 = 12 (2 4)

Course 1

1-5 Mental Math

Additional Example 1A: Using Properties to Add and Multiply Whole Numbers

A. Evaluate 17 + 5 + 3 + 15.

17 + 5 + 3 + 15 Look for sums that are multiples of 10

40

Use the Commutative Property. 17 + 3 + 5 + 15

(17 + 3) + (5 + 15)

Use mental math to add.

20 + 20

Use the Associative Property to make groups of compatible numbers.

Course 1

1-5 Mental Math

Additional Example 1B: Using Properties to Add and Multiply Whole Numbers

B. Evaluate 4 13 5.

4 13 5

Look for products that are multiples of 10

260

Use the Commutative Property.13 4 5

13 (4 5)

Use mental math to multiply.13 20

Use the Associative Property to group compatible numbers.

Course 1

1-5 Mental Math

Try This: Example 1A

A. Evaluate 12 + 5 + 8 + 5.

12 + 5 + 8 + 5 Look for sums that are multiples of 10

30

Use the Commutative Property.12 + 8 + 5 + 5

(12 + 8) + (5 + 5)

Use mental math to add.

20 + 10

Use the Associative Property to make groups of compatible numbers.

Course 1

1-5 Mental Math

Try This: Example 1B

B. Evaluate 8 3 5.

8 3 5 Look for products that are multiples of 10

120

Use the Commutative Property.3 8 5

3 (8 5)

Use mental math to multiply.3 40

Use the Associative Property to group compatible numbers.

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1-5 Mental Math

DISTRIBUTIVE PROPERTY

Words NumbersWhen you multiply a number times a sum, you can• find the sum first and then multiply, or• multiply by each number in the sum and then add.

6 (10 + 4) = 6 14 = 846 (10 + 4) = (6 10) + (6 4) = 60 + 24 = 84

Course 1

1-5 Mental Math

When you multiply two numbers, you can “break apart” one of the numbers into a sum and then use the Distributive Property.

Break the greater factor into a sum that contains a multiple of 10 and a one-digit number. You can add and multiply these numbers mentally.

Helpful Hint

Course 1

1-5 Mental Math Additional Example 2A: Using the Distributive Property

to Multiply

Use the Distributive Property to find the product.

A. Evaluate 6 35.

6 35 = 6 (30 + 5) “Break apart” 35 into 30 + 5.

= 210

Use the Distributive Property.= (6 30) + (6 5)

Use mental math to add.

= 180 + 30 Use mental math to multiply.

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1-5 Mental Math

Additional Example 2B: Using the Distributive Property to Multiply

Use the Distributive Property to find the product.

B. Evaluate 9 x 87.

9 87 = 9 (80 + 7) “Break apart” 87 into 80 + 7.

= 783

Use the Distributive Property.= (9 80) + (9 7)

Use mental math to add.

= 720 + 63 Use mental math to multiply.

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1-5 Mental Math

Try This: Example 2A

Use the Distributive Property to find the product.

A. Evaluate 4 x 27.

4 27 = 4 (20 + 7) “Break apart” 27 into 20 + 7.

= 108

Use the Distributive Property.= (4 20) + (4 7)

Use mental math to add.

= 80 + 28 Use mental math to multiply.

Course 1

1-5 Mental Math

Try This: Example 2B

Use the Distributive Property to find the product.

B. Evaluate 6 43.

6 43 = 6 (40 + 3) “Break apart” 43 into 40 + 3.

= 258

Use the Distributive Property.= (6 40) + (6 3)

Use mental math to add.

= 240 + 18 Use mental math to multiply.

Lesson Quiz

Evaluate.

1. 18 + 24 + 2 + 6 2. 10 5 3

3. 13 + 42 + 7 + 8

Use the Distributive Property to find each

product.

4. 8 12 5. 6 15

6. Angie wants to buy 3 new video games. How

much will she need to save if each game costs

$27?

15050

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70

96

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90

$81

Weekly Review!

Thank you for all of your hard work this week!I am so proud to be your teacher!

Mrs. Burgess