Mental strategies for addition and subraction

Strategies

Pupils should be taught to: recall all addition and subtraction facts for each number up to 20; work out what they need to add to any two-digit number to make 100, then add or subtract any pair of two-digit whole numbers; understand how the commutative and associative laws can be used to do mental addition calculations more efficiently; handle (mentally) particular cases of three-digit and four-digit additions and subtractions by using compensation or other methods; choose and use an appropriate way to calculate and explain their reasoning; use correctly the symbol for ‘equals’.

Here we will look at explanations of

• The associative law for addition
• Counting forwards and backwards in ones, tens, hundreds
• Using multiples of 10 and 100 as stepping stones
• Front-end addition and subtraction
• Compensation in addition and subtraction calculations
• Using multiples of 5 in addition and subtraction
• Relating additions and subtractions to double; and using ‘friendly’ numbers