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Check the Order of Magnitude by Rounding

In this worksheet, students check the order of magnitude of a calculation by rounding first.

'Check the Order of Magnitude by Rounding' worksheet

Key stage:  KS 2

Curriculum topic:   Maths and Numerical Reasoning

Curriculum subtopic:   Place Value

Difficulty level:  

Worksheet Overview

When you use a calculator, you must have a rough idea of the expected size of your answer.

This size is called the order of magnitude and you can get a good idea by rounding off the question first.

 

7840 × 28 is approximately 8000 × 30 which is 240000

24216 - 18947 is approximately 24000 - 19000 = 5000

542 ÷ 18 is approximately 500 ÷ 20 or 25

 

Example

Let's find the order of magnitude for 3.42  × 19.

 

3.42 × 19 lies between
A
and
B
which equal 
C
and
D

 

3.42 × 19 lies between 3 × 19 and 4 × 19.

 

3.42 × 19 lies between
3 × 19
and
4 × 19
which equal 
57
and
76

 

 

Check to see how close you are by doing the calculation on your calculator as well.

 

3.42 × 19 =
64.98

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