Mental addition and subtraction strategies
Maths · Key Stage 2 · The School
Some sums do not need a pencil
Not every sum needs a written method. Some numbers are friendly. 48 add 30 is easy in your head. You just add three tens to 48. A written method would only slow you down here. Knowing when your head is enough is a real skill. It saves time in a test, and it saves time every day.
Bridging through ten
Try 27 add 8. First jump 3, to reach 30. That uses up 3 of the 8. You have 5 left over. Add that 5 on to 30. The answer is 35. Splitting the second number like this is called bridging. It turns one tricky sum into two easy ones.
Counting up to subtract
For 63 take away 28, do not subtract straight away. Count up from 28 to 63 instead. Go from 28 to 30. That is a jump of 2. Then go from 30 to 60. That is a jump of 30. Then go from 60 to 63. That is a jump of 3. Add the jumps together: 2 add 30 add 3 makes 35. Counting up often beats a written method when two numbers sit close together.
Two sums, two strategies
Try 96 add 5 first. Bridge through 100. Add 4 to reach 100. Then add the last 1. The answer is 101. Now try 81 take away 76. The numbers are close, so count up instead. From 76 to 80 is a jump of 4. From 80 to 81 is a jump of 1. Add the jumps: 4 add 1 makes 5. Two different sums used two different strategies. Both were faster than reaching for a pencil.