Lesson 11- Estimation Of Decimals

Objective

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

An estimate is a rough guess. In this lesson, we will learn how to estimate decimals in addition and subtraction questions.

To estimate a decimal, you may quickly round it to the nearest whole number, tenth, hundredth or thousandth before adding or subtracting.

Example 1

Estimate the following decimals.

a) 4.6 + 2.1 b. 5.1 – 3.5

Example 2

Estimate the following decimals(leave your answer to 1 decimal place)

Example 3

Estimate to the nearest hundredth.

a) 13.725 + 3.123 b. 15.123 – 12.281

Solution

NB: The decimals are rounded to 2 decimal places before adding or subtracting.

Unit 10 Lesson 11: Exercise 1

Estimate the following. Leave your answers as whole numbers.

1) 21 2) 6 3) 70 4) 66 5) 32
6) 5 7) 9 8) 28 9) 50 10) 5

Unit 10 Lesson 11: Exercise 2

Estimate these decimals leaving your answers to 1 d.p

1) 9.0 2) 6.9 3) 2.0 4) 10.4 5) 5.8
6) 34.5 7) 34.9 8) 41.1 9) 16.5 10) 3247.5

Unit 10 Lesson 11: Exercise 3

Estimate these decimals. Your answers should be left at 2 decimal places.

1) 770.51 2) 6.38 3) 33.81 4) 133.88 5) 53.83
6) 70.32 7) 10.18 8) 7.14 9) 4.50 10) 11.56

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