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# How many significant figures do you round a number off by when estimating an answer to a calculation?

By Lisa Kelly on the 11th of June, 2012

Estimating is actually very easy, so long as you don't over complicate it. Its really just a two step process:

1. ROUND EVERYTHING OFF to nice easy CONVENIENT NUMBERS

2. Then WORK OUT THE ANSWER using these nice easy numbers....that's it!

Let's go through a practice question.

'Estimate the answer to the following equation: 647 / (4.8×9.7)'

In this case, when they ask you to estimate, they actually want you to round the equation off to each number's nearest significant figure. 647 can be rounded up to 650, a much easier number for calculations, and 4.8 and 9.7 can be rounded up to 5 and 10 respectively, making the equation...

650 / (5×10)

Which should now be much easier to do without a calculator!

## Follow the links below to see how this topic has appeared in past exam papers

AQA Unit 2 November 2012 (H) - Page 2, Question 1

AQA Unit 2 March 2011 (H) - Page 6, Question 7

AQA Unit 2 June 2011 (H) - Page 2, Question 2

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