Holt CA Course 1

6-3 Estimating with Percents

NS1.4 Calculate given percentages of quantities and solve problems involving discounts at sales, interest earned, and tips.Also covered: NS2.1

California Standards

Holt CA Course 1

6-3 Estimating with Percents

The table shows common percents and their fraction equivalents. You can estimate a percent of a number by substituting a fraction that is close to a given percent.

Fraction

Percent 10% 20% 25% 50%33 %13 66 %

23

15

14

13

12

23

110

Holt CA Course 1

6-3 Estimating with Percents

Use a fraction to estimate 27% of 63.

Additional Example 1: Using Fractions to Estimate Percents

27% of 63 14

63

14

60

1527% of 63 is about 15.

Compatible numbers are close to the numbers in the problem and help you use mental math to find a solution.

Remember!

Think: 27% is about 25% and

25% is equivalent to .14

Change 63 to a compatible number.

Multiply.

Holt CA Course 1

6-3 Estimating with Percents

Use a fraction to estimate 48% of 91.

Check It Out! Example 1

48% of 91 12

91

12

90

45

48% of 91 is about 45.

Think: 48% is about 50% and

50% is equivalent to .12

Change 91 to a compatible number.

Multiply.

Holt CA Course 1

6-3 Estimating with Percents

Tara’s T’s is offering 2 T-shirts for $16, while Good-T’s is running their buy one for $9.99, get one for 50% off sale. Which store offers the better deal?

Additional Example 2: Consumer Math Application

First find the discount price for 2 t-shirts at Good T’s.

50% of $9.99 =12 $9.99

12

$10

$5

The second shirt cost approximately $5. Since $10 + $5 = $15, the 2 T-shirts for $15 at Good-T’s is the better deal.

Think: 50% is equivalent to .12

Change $9.99 to a compatible number.

Multiply.

Holt CA Course 1

6-3 Estimating with PercentsCheck It Out! Example 2

First find the discount on the notebook at Billy’s Office Supply.

25% of $9.75 = 14

$9.75

14

$10

$2.50

The discount is approximately $2.50. Since $10 – $2.50 = $7.50, the notebook from K’s Office Supply Store is the better deal.

Think: 25% is equivalent to .14

Change $9.75 to a compatiblenumber.

Multiply.

Billy’s Office Supply Store is offering 25% off a leather notebook, originally priced at $9.75. K’s Office Supply Store offers the same notebook, not on sale, at $7.00. Which store offers the better deal?

Holt CA Course 1

6-3 Estimating with Percents

Another way to estimate percents is to find1% or 10% of a number. You can do thisby moving the decimal point in the number.

1% of 45 = 10% of 45 =

To find 1% of a number, move the decimal point two places to the left.

To find 10% of a number, move the decimal point one place to the left.

. .0 45. 45.

Holt CA Course 1

6-3 Estimating with Percents

Use 1% or 10% to estimate the percent of each number.

Additional Example 3: Estimating with Simple Percents

A. 4% of 18

18 is about 20, so find 4% of 20.

1% of 20 = 20.

4% of 20 = 4 0.2 = 0.8

4% of 18 is about 0.8.

4% equals 4 · 1%.

.

Holt CA Course 1

6-3 Estimating with Percents

Use 1% or 10% to estimate the percent of each number.

Additional Example 3: Estimating with Simple Percents

B. 29% of 80

29% is about 30, so find 30% of 80.

10% of 80 = 80.

30% of 80 = 3 8.0 = 24.0

29% of 80 is about 24.

30% equals 3 · 10%.

.

Holt CA Course 1

6-3 Estimating with Percents

Use 1% or 10% to estimate the percent of each number.

Check It Out! Example 3

A. 5% of 14

14 is about 15, so find 5% of 15.

1% of 15 = 15.

5% of 15 = 5 0.15 = 0.75

5% of 14 is about 0.75.

5% equals 5 · 1%.

.

Holt CA Course 1

6-3 Estimating with Percents

Use 1% or 10% to estimate the percent of each number.

Check It Out! Example 3

B. 21% of 60

21% is about 20, so find 20% of 60.

10% of 60 = 60.

20% of 60 = 2 6.0 = 12.0

21% of 60 is about 12.

20% equals 2 · 10%.

.

Holt CA Course 1

6-3 Estimating with Percents

Tim spent $58 on dinner for his family. About how much money should he leave for a 15% tip?

Additional Example 4: Consumer Math Application

Since $58 is about $60, find 15% of $60.

15% = 10% + 5%

10% of $60 = $6

5% of $60 = $6 ÷ 2 = $3

$6 + $3 = $9

Tim should leave about $9 for a 15% tip.

Think: 15% is 10% + 5%.

5% is of 10% so divide $6 by 2.

12

Add the 10% and 5% estimates.

Holt CA Course 1

6-3 Estimating with Percents

Amanda spent $12 on a hair cut. About how much money should she leave for a 15% tip?

Check It Out! Example 4

Since $12 is about $10, find 15% of $10.

15% = 10% + 5%

10% of $10 = $1

5% of $10 = $1 ÷ 2 = $0.50

$1 + $0.50 = $1.50

Amanda should leave about $1.50 for a 15% tip.

Think: 15% is 10% + 5%.

5% is of 10% so divide $1 by 2.

12

Add the 10% and 5% estimates.