Pre-Algebra

8-2 Finding Percents8-2 Finding Percents

Pre-Algebra

Warm UpWarm Up

Problem of the DayProblem of the Day

Lesson PresentationLesson Presentation

Pre-Algebra

8-2 Finding Percents

Warm Up Pssa TestedRewrite each value as indicated.

1. as a percent

2. 25% as a fraction

3. as a decimal

4. 0.16 as a fraction

48%

0.375

Pre-Algebra

8-2 Finding Percents

425

24 50

3 8

14

Pre-Algebra

8-2 Finding Percents

Learn to find percents.

Pre-Algebra

8-2 Finding Percents

Finding the Percent One Number Is of Another

What percent of 220 is 88?

Pre-Algebra

8-2 Finding Percents

Finding the Percent One Number Is of Another

What percent of 19 is 95?

Pre-Algebra

8-2 Finding Percents

Finding the Percent One Number Is of Another

18 is what percent of 60?

Pre-Algebra

8-2 Finding Percents

Pre-Algebra

8-2 Finding Percents

What percent of 102 is 17?

13 is what percent of 52?

Pre-Algebra

8-2 Finding Percents

Eddie weighs 160 lb, and his bones weigh 24 lb. Find the percent of his weight that his bones are.

Finding the Percent One Number Is of Another

Think: What number is to 100 as 24 is to 160?

=number

100 partwhole Set up a proportion.

Substitute. n

100 24160

=

n 160 = 100 24

160n = 2400

Find the cross products.

Method 2: Set up a proportion to find the percent.

Pre-Algebra

8-2 Finding Percents

Additional Example 1 Continued

n = 15

= 15

100 24160

The proportion is reasonable.

Solve for n.160 2400n =

So 15% of Eddie’s weight is bone.

Pre-Algebra

8-2 Finding Percents

B. Jamie weighs 140 lb, and his bones weigh 21 lb. Find the percent of his weight that his bones are.

Think: What number is to 100 as 21 is to 140?

=number

100 partwhole Set up a proportion.

Substitute. n

100 21140

=

n 140 = 100 21

140n = 2100

Find the cross products.

Try This: Example 1B

Method 2: Set up a proportion to find the percent.

Pre-Algebra

8-2 Finding Percents

n = 15

The proportion is reasonable.

Solve for n.140 2100n =

So 15% of Jamie’s weight is bone.

= 15

100 21140

Pre-Algebra

8-2 Finding Percents

Additional Example 2A: Finding a Percent of a Number

A. After a drought, a reservoir had only 66 % of the average amount of water. If the average amount of water is 57,000,000 gallons, how much water was in the reservoir after the drought?

23

Choose a method: Set up an equation.

Think: What number is 66 % of 57,000,000?23

w = 66 % 57,000,000 Set up an equation.23

w = 57,000,000 66 % is equivalent to . 23

23

23

Pre-Algebra

8-2 Finding Percents

Additional Example 2A Continued

The reservoir contained 38,000,000 gallons of water after the drought.

w = = 38,000,000 114,000,000

3

Pre-Algebra

8-2 Finding Percents

Additional Example 2B: Finding Percents

B. Ms. Chang deposited $550 in the bank. Four years later her account held 110% of the original amount. How much money did Ms. Chang have in the bank at the end of the four years?

Choose a method: Set up a proportion.

=110

100 a

550Set up a proportion.

110 550 = 100 a Find the cross products.

60,500 = 100a

Pre-Algebra

8-2 Finding Percents

Additional Example 2B Continued

605 = a Solve for a.

Ms. Chang had $605 in the bank at the end of the four years.

Pre-Algebra

8-2 Finding Percents

Try This: Example 2B

B. Mr. Downing deposited $770 in the bank. Four years later his account held 120% of the original amount. How much money did Mr. Downing have in the bank at the end of the four years?

Choose a method: Set up a proportion.

=120

100 a

770 Set up a proportion.

120 770 = 100 a Find the cross products.

92,400 = 100a

Pre-Algebra

8-2 Finding Percents

Try This: Example 2B Continued

924 = a Solve for a.

Mr. Downing had $924 in the bank at the end of the four years.

Pre-Algebra

8-2 Finding Percents

What percent of 88 is 13?

90 is what percent of 75?

What percent of 4 is 6?

Pre-Algebra

8-2 Finding Percents

Lesson Quiz

Find each percent to the nearest tenth.

1. What percent of 33 is 22?

2. What percent of 300 is 120?

3. 18 is what percent of 25?

4. The volume of Lake Superior is 2900 mi3 and

the volume of Lake Erie is 116 mi3. What percent

of the volume of Lake Superior is the volume of

Lake Erie?

40%

66.7%

72%

4%

Pre-Algebra

8-2 Finding Percents

Help!

Pre-Algebra

8-2 Finding Percents

Learned to find percents.

Pre-Algebra

8-2 Finding Percents

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