8-1 Percent and Estimation

Pages 334-337

Indicator(s) N8 Develop and analyze algorithms for computing with percents and demonstrate fluency in use.

To estimate the percent of a number…

…you can use a fraction or a multiple of 10% or 1%.

Example 1Use a fraction to estimate 77% of 800.

77% is about 75% or .

77% of 800 ≈ × 800

≈ 600So, 77% of 800 is about 600.

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Example 2

Percents greater than 100. Estimate 137% of 50.137% is more than 100%,

so 137% is going to be greater than 50.

137% is about 140%.

140% of 50 = (100% × 50) + (40% × 50)

= (1 × 50) + ( × 50)

= 50 + 20 = 70

So, 137% of 50 is about 70.

Percents greater than 100

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Example 3

Percents less than 1. Estimate 0.5% of 692.

0.5% is half of 1%.

692 is about 700

To find 1% of 700, change % to decimal and multiply.

1%= 0.01 SO… = 0.01 × 700

= 7

One half of 7 is 7 × or 3.5

So, 0.5% of 692 is about 3.5.

Percents less than 1

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Example 4

Estimate 59% of 500.

10% of 500 is 50.

59% is about 60%.

60% of 500 is 6 × 10%.

6 × 50 = 300

So, 59% of 500 is about 300.

Estimate by using 10%

8-1 b

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