Lesson 10- Estimating Decimal Sums and Differences

Objective:

At the end of this lesson, students should be able to estimate answers to questions involving decimal addition and/or subtraction.

To estimate means to make an informed guess. Decimals can be estimated by first rounding the decimal numbers involved to the nearest whole number, tenth, hundredth or thousandth before adding or subtracting.

Example 1

Estimate these decimals to the nearest unit/whole.

Example 2

Estimate these to the nearest tenth.

Example 3

Estimate the following. Leave your answer to 2 decimal places.

Example 4

Estimate the decimals below to the nearest thousandth.

Unit 10 Lesson 10: Exercise 1

Estimate to the nearest whole.

1) 30 2) 9 3) 9g 4) 147m 5) 22ml
6) 24cm 7) £21 8) £53 9) £79 10) £65

Unit 10 Lesson 10: Exercise 2

Work out the following by estimating. Leave your answers to 1 decimal place.

Estimate to the nearest hundredth

1) 81.8 2) 29.9 3) 17.0 4) 254.6 5) 12.8
6) 22.5 7) 7.59 8) 46.42 9) 5.05 10) 36.16

Unit 10 Lesson 10: Exercise 3

1) 14.746 2) 7.975 3) 6.840 4) 3.052 5) 10.111
6) 19.003 7) 2.183 8) 14.509 9) 10.533 10) 5.434

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