__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. 5.6 – 3.5

__Solution__

a) 4.6 + 2.1 = 6.7

Estimate = 5+2 = 7

b)5.6 – 3.5= 2.1

Estimate = 6 – 4 = 2

__Example 2__

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

a)6.49 + 1.25 b. 9.35 – 4.35

__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.**

a) 13.725 + 3.123 = 16.848

Estimate: 13.73 + 3.12 = 16.85

b) 15.123 – 12.281 = 2.842

Estimate = 15.12 – 12.28 = 2.84

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