1. Preview
Warm Up
California Standards
Lesson Presentation

2. Warm Up
Multiply.
 20
 15
 25
 18
 76 1
4.8
1.5
13.5
25.84

3. 6-4 Percent of a Number Standards California
NS1.4 Calculate given percentages of quantities and solve problems involving discounts at sales, interest earned, and tips.
Also covered: NS2.4

4. The human body is made up mostly of water
The human body is made up mostly of water. In fact, about 67% of a person’s total (100%) body weight is water. If Cameron weighs 90 pounds, about how much of his weight is water?
Recall that a percent is a part of 100. Since you want to know the part of Cameron’s body that is water, you can set up and solve a proportion to find the answer.
Part 67 = n
100 90
Whole

5. Additional Example 1: Using Proportions to Find Percents of Numbers
Find the percent of each number.
A. 30% of 50 30
100 n 50 =
Write a proportion.
30 · 50 = 100 · n
Set the cross products equal.
1,500 = 100n
Multiply.
1,500
100n
Divide each side by 100. =
100
100
15 = n
30% of 50 is 15.

6. When solving a problem with a percent greater than 100%, the part will be greater than the whole.
Helpful Hint

7. Additional Example 1: Using Proportions to Find Percents of Numbers
Find the percent of each number.
B. 200% of 24
200
100 n 24 =
Write a proportion.
200 · 24 = 100 · n
Set the cross products equal.
4,800 = 100n
Multiply.
4,800
100n =
Divide each side by 100.
100
100
48 = n
200% of 24 is 48.

8. Check It Out! Example 1
Find the percent of each number.
A. 40% of 40 40
100 n 40 =
Write a proportion.
40 · 40 = 100 · n
Set the cross products equal.
1,600 = 100n
Multiply.
1,600
100n =
Divide each side by 100.
100
100
16 = n
40% of 40 is 16.

9. Check It Out! Example 1
Find the percent of each number.
B. 150% of 64
150
100 n 64 =
Write a proportion.
150 · 64 = 100 · n
Set the cross products equal.
9,600 = 100n
Multiply.
9,600
100n =
Divide each side by 100.
100
100
96 = n
150% of 64 is 96.

10. In addition to using proportions, you can find a percent of a number by using decimal equivalents.

11. Write the percent as a decimal and multiply.
Additional Example 2: Using Decimal Equivalents to Find Percents of Numbers
Find the percent of the number. Check whether your answer is reasonable.
A. 9% of 80
9% of 80 = 0.09 · 80
Write the percent as a decimal and multiply.
= 7.2
Check
Since 10% of 80 = 8, a reasonable answer for 9% of 80 is 7.2.
20%
40%
60%
80%
100% 60 80 20 40 9%
7.2

12. Additional Example 2: Using Decimal Equivalents to Find Percents of Numbers
Find the percent of the number. Estimate
to check whether your answer is reasonable.
B. 3% of 12
3% of 12 = 0.03 · 12
Write the percent as a decimal and multiply.
= 0.36
Check
5% · 12 = 0.6, so 3% of 12 is a little less than 0.6. Thus 0.36 is a reasonable answer.

13. Write the percent as a decimal and multiply.
Check It Out! Example 2
Find the percent of the number. Check whether your answer is reasonable.
A. 21% of 40
21% of 40 = 0.21 · 40
Write the percent as a decimal and multiply.
= 8.4
Check
Since 20% of 40 = 8, a reasonable answer for 21% of 40 is 8.4.
20%
40%
60%
80%
100% 30 40 10 20
21%
8.4

14. Check It Out! Example 2
Find the percent of the number. Estimate
to check whether your answer is reasonable.
B. 6% of 18
6% of 18 = 0.06 · 18
Write the percent as a decimal and multiply.
= 1.08
Check
5% · 20 = 1, so 6% of 18 is close to 1. Thus 1.08 is a reasonable answer.

15. Additional Example 3: Geography Application
The estimated world population in 2001 was 6,157 million. About 40% of the people were 19 or younger. What was the approximate number of people 19 or younger, to the nearest million?
Find 40% of 6,157 million.
0.40 · 6,157
Write the percent as a decimal.
= 2,462.8
Multiply.
≈ 2,463
Round to the nearest whole number.
The number of people 19 or younger was about 2,463 million.

16. Write the percent as a decimal.
Check It Out! Example 3
The estimated world population in 2001 was 6,157 million. About 60% of the people were above 19 years of age. What was the approximate number of people 19 or older, to the nearest million?
Find 60% of 6,157 million.
0.60 · 6,157
Write the percent as a decimal.
= 3,694.2
Multiply.
≈ 3,694
Round to the nearest whole number.
The number of people 19 or older was about 3,694 million.

17. Lesson Quiz Find the percent of each number. 1. 25% of 8 2. 40% of 110
Find the percent of each number. Check whether your answer is reasonable.
3. 150% of 96
4. 0.3% of 120
5. Whitmer Middle School has 850 students. If 42% of the students bought lunch on Monday, how many student bought lunch on Monday? 2 44
144
0.36
357