USING PERCENTS AND CALCULATING PERCENT

CHANGE

Objectives: SWBAT do calculations using percents. SWBAT find percents of increase and decrease. SWBAT use percent change to find initial or final values.

Percents

A percent is a ratio out of 100. Example: In the Uplift class of 2012,

about 64% of the students are female. If there are 96 students in the class, how many girls are there?

64 = x 64*96 = 100x100 96 6144 = 100x

61.44 = xThere are 61 girls in the class.

Ex. : State whether each percent of change is a percent of decrease or increase. Then find the percent of change.

1. initial: 32 final: 40

40 – 32 = 8

8 = 0.25 -> 25%32

2. initial: 20 final: 4

4 – 20 = -16

-16 = - 0.8 = -80%20

Vocabulary

Percent: a fraction out of 100 Percent of change: an increase or

decrease expressed at a percent. Percent of increase: the percent by

which new number is greater than the original number.

Percent of decrease: the percent by which the new number is less than the original number.

Percent of Change Formula

Percent of Change: final amount – initial amount

initial amount

You TRY!!!!

3. initial: 72 final: 36

36 – 72 = - 36

-36 = -0.5 = - 50%72

4. initial: 45 final: 50

50 – 45 = 5

5 = 0.111 = 11.1%45

Using Percent Change

To calculate final value, use (1 + c) * initial value.

c = % change written as a decimal Example: A store is having a 20% off sale.

How much does a shirt that was $60 cost?

Initial value: $60 Percent change: -20% = -.2 (1 + -.2) * $60 = 0.8 * $60 = $48

Ex: Using Percent Change1. The price a used-book store pays to buy

a book is $5. The store sells the book for 28% above the price that it pays for the book. What is the selling price of the $5 book?

Ex: Find the total price of each item.

1. Software: $39.50

Sales tax: 6.5%

2. Compact disc: $15.99

sales tax: 5.75%

Ex: Find the discounted price of each item.

1. jeans: $45.00 discount: 25%

2. book: $19.95 discount: 33%

Ex: Find the final price of each

1. lamp: $120.00 discount: 20% tax: 6%

2. camera: $58.00 discount: 25% tax: 6.5%

In 1987, the United States had 2 million active-duty military personnel. By 2000, there were only 1.4 million active-duty military personnel. What was the percent of decrease?

Practice

Practice

In order for a food to marked “reduced fat,” it must have at least 25% less fat than the same full-fat food. If one ounce of reduced fat chips has 6 grams of fat, what is the least amount of fat in one ounce of regular chips?