Mental addition and subtraction for the 11 plus

Two friendly tricks. First, bridge through the next ten. 68 needs two to reach 70. Take two from the 25, leaving 23. 70 and 23 is 93. Second, compensate. To add 299, add 300 and take one back. Round to a friendly number, then pay the difference.

197 plus 36. Two hundred is close to 197, three short. So 200 plus 36 is 236. We added three too many, so take three back. 233.

The trap is adjusting the wrong way. 197 is less than 200, so rounding up adds too much. The answer must be smaller than 236, not bigger. If the carried ten goes missing, you get an answer ten short. Ask: should my answer be higher or lower than the friendly one?

Part of the Arithmetic topics for the 11+.

• 2.2Column additionCarry the ten, every time
• 2.3Column subtractionHow to borrow from a zero
• 2.4Multiplication tablesBuild the facts you cannot remember
• 2.5Short multiplicationMultiply first, then add the carry
• 2.6Long multiplicationTwo small jobs and one zero
• 2.7DivisionEvery digit needs an answer above it
• 2.8Order of operationsOne sum, one agreed order

Every 11 plus maths topic