What is the sum of….?
What is the total of….?
What must I add to …. to make ….?
How many more than … is …?
How many less than … is …?
It is very useful to spend some time on asking children how they approach these questions, ‘in their heads’. For example:
‘What must I add to 7 to make 20?’ can be approached in several ways.
One way is to add on 3 to make 10 and then 10 more to make 20.
Another way is to add 10 and then count on 3.
A further method would be to take 10 from 20 and then count back 3 more.
By asking children to explain their methods it makes them think about what they have done and they will often see that there is a more efficient method than the one they used. The ultimate aim of this is to develop quick and efficient methods which produce correct answers.