You have already found percents using the percent proportion. (Lesson 7–3)

• Compute mentally with percents.

• Estimate with percents.

Use a Fraction to Compute Mentally

A. Find 50% of 46 mentally.

Answer: 50% of 46 is 23.

THINK:

THINK:

Use a Fraction to Compute Mentally

= 6

A. 41

B. 164

C. 16

D. 40

A. Find 50% of 82 mentally.

A. 6

B. 4

C. 16

D. 48

B. Find 25% of 24 mentally.

Use Decimals to Compute Mentally

A. Compute 10% of 54 mentally.

Answer: 5.4

10% of 54 = 0.1 ● 54 or 5.4

Use Decimals to Compute Mentally

B. Compute 1% of 219 mentally.

Answer: 2.19

1% of 219 = 0.01 ● 219 or 2.19

Use Decimals to Compute Mentally

C. Compute 20% of 50 mentally.

Answer: 10

First, find 10% of 50 = 0.1 ● 50 or 5

Then, 20% is 2 ● 10%, so 20% of 50 = 2(10% of 50)

= 2(5)

= 10

Use Decimals to Compute Mentally

D. Compute 15% of 40 mentally.

Answer: 6

First, find 10% of 40 = 0.1 ● 40 or 4

= 2

Think of 15% as 10% + 5%

Finally add (10% of 40) + (5% of 40) = 4 + 2

= 6

A. 0.089

B. 0.89

C. 8.9

D. 890

A. Find 10% of 89 mentally.

A. 0.0543

B. 0.543

C. 5.43

D. 54.3

B. Find 1% of 543 mentally.

A. 56

B. 8

C. 24

D. 16

C. Find 30% of 80 mentally.

A. 6

B. 3

C. 9

D. 30

C. Find 15% of 60 mentally.

Compute Mentally

SHOPPING Garrett is shopping for a new video game. The original price of the game is $60.00. The game is 10% off. How much will Garrett save?

Find 10% of $60.

10% of 60 = 0.10 ● 60 Move the decimal pointone place to the left.

= 6

Answer: Garrett will save $6.

A. $4.20

B. $21.00

C. $42.00

D. $84.00

John has a coupon for a 10% discount. If he buys a television with a regular price of $420, how much will he save?

Estimate Percent of a Number

A. Estimate 22% of 494.

Answer: So, 22% of 494 is about 100.

Estimate Percent of a Number

B.

So,

Estimate Percent of a Number

C. Estimate 49% of 61.

Answer: So, 49% of 61 is about 30.

61 is about 60.

Estimate Percent of a Number

D. Estimate 155% of 38.

Answer: So, 155% of 38 is about 40 + 20 or 60.

155% is about 150%. 38 is about 40.

100% of 40 is 40. 50% of 40 is 20.

A. 100

B. 152

C. 160

D. 80

A. Estimate 38% of 400.

A. 25

B. 4.964

C. 4

D. 5

B. Estimate % of 2482.

C. Which is the best estimate for 26% of 78?

A. 10

B. 20

C. 25

D. 30

A. 135

B. 46.5

C. 49.29

D. 180

D. Estimate 153% of 93.