Step 5 Objective

Check a result by considering whether it is of the right order of magnitude and by working the problem backwards.

Examples of what pupils should know and be able to do

Probing questions

Roughly, what answer do you expect to get? How did you come to that estimate? Do you think your estimate is higher or lower that the real answer? Explain why.

How would you use inverse operations to check that a calculation is correct?

What if pupils find this a barrier?

It can be helpful to give pupils some worked examples to mark and to identify the mistakes.

Encourage pupils to approximate first before working out answers.

Refer to Teaching Mental Calculation Strategies to L5 pp. 55-60. - Acrobat pdf document (50Kb)