Whilst in year 1 and 2 the expectation is that children will know which pairs of numbers will make 10, by year 3 they are expected to be able to work out quickly pairs of numbers that make 100.
Look at: 47 + ? = 100.
It has never been made clear exactly what is meant by knowing these facts: certainly I would suggest that a quick mental sum should be sufficient rather than actually knowing that 47 needs another 53 to make 100. In other words what needs to be known is:
1. pairs that make 10
2. pairs of whole tens that make 100.
So a child could quickly add the 3 to make the next whole ten (50) and then 50 to make 100.
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