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