Chapter 2Lesson 3

Objective

•Round decimal numbers•Use rounding to estimate an answer

Vocabulary

•Rounding (approximation)•Estimate

Visual Rounding

Example 1

Round 16.0973 to the nearesta. ten b. tenth c. hundredth

a. 16 is closer to 20 than 10, so 16.0973 ≈ 20

b. 16.0973…the 9 brings the 0 to a 1, so 16.0973 ≈ 16.1

c. the 9 is in the hundredth place followed by a 7, so 16.0973 is 16.10

Why Round?

Rounding is often used as a quick check on calculations. In general, we estimate by rounding to the highest place value of the smaller number for all operations. As a result, our estimated answer should be reasonably close to the exact answer.

Example 2

Find an estimated answer for each operation.

a. 386 + 54 = 390 + 50 = 440

b. 2.849 – 0.154 = 2.8 – 0.2 = 2.6

c. 32.9 x 8.7 = 33 x 9 = 297

d. 253 ÷ 12 = 250 ÷ 10 = 25

Guided Practice

Round to the nearest ten.1) 27.82) 13.2

Round to the nearest tenth.3) 75.634) 4.45

Guided Practice

Round to the nearest hundredth.5) 112.3476) 77.012

Round to the nearest thousandth.7) 0.34528) 12.10103

Homework

Pg. 49; 2-24 (even)

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