When working out how many more to make a number up to 100 it is important not to mix up two different ways of doing it. Let’s take the question:
‘How many more is there from 45 to 100?’
One way of doing this is to add 5 to 45, making 50 and then counting on 50 to make 100. That’s 55 in total.
Another way is to count on in tens from 45 to 95, which is 50, and then add on the extra 5, again making 55.
Watch out for children who get slightly confised, add on from 40 to 100, making 60 and then adding on another 5. This method will always result in ten more than the correct answer.
The ultimate aim of questions like these is to make the answers second nature or even to know them ‘off by heart’.
This page can be found in our Year 3, Calculating section.