DEVELOPING AN UNDERSTANDING OF SUBTRACTION :  The process of subtraction is the reverse of that of addition. Adding more to a collection to make it bigger is just the reverse of taking away or removing some to make it smaller. Let us look at the kinds of situations in which children would have to recognise that the solution of the problem requires that to subtract. Problems involving subtraction are more complex for children to handle than those involving addition. This is because they have to identify which quantity has to be taken away from which. This is very important because so far they were exposed to addition, where 2 + 3 = 3 + 2. But 9 - 3 is not the same as 3 - 9, that is, subtraction is, not commutative.