11+ Mental Maths: 8 Shortcuts That Save Time in the Exam
By Simply Eleven Plus · Updated 25 October 2026 · 5 min read
11+ maths papers are tightly timed, so a child who can work quickly in their head has more time for the hard questions. These shortcuts are all exact, not estimates, and each one is easy to check.
1. Multiply by 5: multiply by 10, then halve
Example
48 × 5 = 480 ÷ 2 = 240
2. Multiply by 9: multiply by 10, then take away the number
Example
37 × 9 = 370 − 37 = 333
3. Multiply by 25: multiply by 100, then divide by 4
Example
36 × 25 = 3600 ÷ 4 = 900
4. Multiply a two-digit number by 11: add the digits and put the total in the middle
Example
34 × 11: 3 + 4 = 7, so the answer is 3, 7, 4 = 374
78 × 11: 7 + 8 = 15. Put the 5 in the middle and carry the 1: 7 + 1 = 8, so the answer is 858
5. Halve one number and double the other
Example
16 × 25 = 8 × 50 = 4 × 100 = 400
6. Percentages: find 10%, then build up
Example
35% of 60: 10% is 6, so 30% is 18. 5% is half of 10%, so 3. 18 + 3 = 21
7. Fractions of amounts: divide by the bottom, multiply by the top
Example
3/5 of 45: 45 ÷ 5 = 9, and 9 × 3 = 27
8. Round, then adjust
Example
198 + 67 = 200 + 67 − 2 = 265
£4.99 × 3 = £15 − 3p = £14.97
Practise it
The method only sticks with practice. Try arithmetic questions on Simply Eleven Plus, free to start, with instant marking and an explanation for every answer, or sit a free live mock exam to practise under real exam conditions.
Free 11+ live mock exams
Let your child sit a real-time, timed mock paper online, then go through the trickiest questions together. It’s free.