Holt CA Course 1

6-4 Percent of a Number6-4 Percent of a Number

NS1.4 Calculate given percentages of quantities and solve problems involving discounts at sales, interest earned, and tips.Also covered: NS2.4

California Standards

Holt CA Course 1

6-4 Percent of a Number

Vocabulary:

Percent of a Number

Holt CA Course 1

6-4 Percent of a Number

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 Part100 90Whole Whole

Holt CA Course 1

6-4 Percent of a Number

Find the percent of each number.

Teacher Example 1: Using Proportions to Find Percents of Numbers

A. 30% of 5030

100= n

5030 · 50 = 100 · n

1,500 = 100n

1,500 100 100

= 100n

15 = n

30% of 50 is 15.

Write a proportion.

Set the cross products equal.

Multiply.

Divide each side by 100.

Holt CA Course 1

6-4 Percent of a Number

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

Helpful Hint

Holt CA Course 1

6-4 Percent of a NumberTeacher Example 1: Using Proportions to Find Percents of

NumbersFind the percent of each number.

B. 200% of 24200100

= n24

200 · 24 = 100 · n

4,800 = 100n

4,800 100 100

= 100n

48 = n

200% of 24 is 48.

Write a proportion.

Set the cross products equal.

Multiply.

Divide each side by 100.

Holt CA Course 1

6-4 Percent of a Number

Find the percent of each number.

Student Practice 1:

A. 40% of 40

40100

= n40

40 · 40 = 100 · n

1,600 = 100n

1,600 100 100

= 100n

16 = n

40% of 40 is 16.

Write a proportion.

Set the cross products equal.

Multiply.

Divide each side by 100.

Holt CA Course 1

6-4 Percent of a NumberStudent Practice 1:

Find the percent of each number.

B. 150% of 64

150100

= n64

150 · 64 = 100 · n

9,600 = 100n

9,600 100 100

= 100n

96 = n

150% of 64 is 96.

Write a proportion.

Set the cross products equal.

Multiply.

Divide each side by 100.

Holt CA Course 1

6-4 Percent of a Number

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

Holt CA Course 1

6-4 Percent of a Number

Find the percent of the number. Check whether your answer is reasonable.

Teacher Example 2: Using Decimal Equivalents to Find Percents of Numbers

A. 9% of 80

9% of 80 = 0.09 · 80

= 7.2Check

Since 10% of 80 = 8, a reasonable answer for 9% of 80 is 7.2.

Write the percent as a decimal and multiply.

0 20% 40% 60% 80% 100%

0 60 8020 40

9%

7.2

Holt CA Course 1

6-4 Percent of a Number

Teacher Example 2: Using Decimal Equivalents to Find Percents of Numbers

Find the percent of the number. Estimateto check whether your answer is reasonable.

B. 3% of 12

3% of 12 = 0.03 · 12

= 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.

Write the percent as a decimal and multiply.

Holt CA Course 1

6-4 Percent of a Number

Find the percent of the number. Check whether your answer is reasonable.

Student Practice 2:

A. 21% of 40

21% of 40 = 0.21 · 40

= 8.4Check

Since 20% of 40 = 8, a reasonable answer for 21% of 40 is 8.4.

Write the percent as a decimal and multiply.

0 20% 40% 60% 80% 100%

0 30 4010 20

21%

8.4

Holt CA Course 1

6-4 Percent of a Number

Student Practice 2:

Find the percent of the number. Estimateto check whether your answer is reasonable.

B. 6% of 18

6% of 18 = 0.06 · 18

= 1.08

Check

5% · 20 = 1, so 6% of 18 is close to 1. Thus 1.08 is a reasonable answer.

Write the percent as a decimal and multiply.

Holt CA Course 1

6-4 Percent of a NumberTeacher Example 3: Consumer Math

Write the percent as a decimal.

Multiply.

Round to the nearest whole number.

Show Style is discounting everything in the store by 25%. What is the sale price of a pair of flip-flops that was originally priced at $10?

Holt CA Course 1

6-4 Percent of a NumberStudent Practice 3:

Write the percent as a decimal.

Multiply.

Round to the nearest whole number.

A store that sells sports souvenirs is offering a 30% discount on all items. The tags on the itemsshow the original prices. Find the amount of discountOn the figurine shown.

Holt CA Course 1

6-4 Percent of a NumberLesson 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?

44

2

144

0.36

357