Estimating With Percents

6-2

*Notes 27

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

Fraction

Percent 10% 20% 25% 50%33 %13 66 %2

3

15

14

13

12

23

110

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.

Use a fraction to estimate 48% of 91.

Check It Out: Example 1

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 half price 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

$5The 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.

Check It Out: Example 2

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?

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.

. .45. 45.

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

Additional Example 3A: Estimating with Simple Percents

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%.

.

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

Additional Example 3B: Estimating with Simple Percents

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%.

.

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

Check It Out: Example 3A

5% of 14

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

Check It Out: Example 3B

21% of 60

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.

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

Check It Out: Example 4