Mental strategies for addition and subraction

How important is mental calculation - part 2?

Remember that when formal written methods have been taught, encourage pupils still to look for an easier way to do additions and subtractions by mental and informal methods first, before resorting to formal written algorithms.

The decision as to which strategy to employ is guided by the actual numbers in the problem. For example, very few of us would use the same strategy for calculating 201 – 20 and 101 -197. The first we might do essentially by counting back in tens from 201, and the second by counting on from 197. Both of these are very simple subtractions, of course, when written down horizontally and done by mental methods.

A good suggestion is that pupils should be thoroughly confident in additions and subtractions written in horizontal format, using mental and informal strategies, before they are introduced to the vertical layout algorithms. Greater sharing of such methods, through open discussion and specific teaching of some of the key mental strategies, will undoubtedly lead to greater confidence with number.