About this quiz

Mental maths is like a muscle: the more you use it, the quicker it gets. This quiz gives you twenty quick sums, from times tables and percentages to a few classic trick questions, all designed to be done in your head.

It starts gently and builds up. After every answer you’ll get a quick shortcut or trick for working it out, so you can be faster next time.

Answers explained

Show the answers (spoilers)

  1. What is 7 × 8?

    56. Remember “5, 6, 7, 8”: 56 = 7 × 8.

  2. What is 15 + 27?

    42. Add 30 to get 45, then take away 3.

  3. What is 100 − 37?

    63. Count up from 37: 3 gets you to 40, then 60 more makes 100. 3 + 60 = 63.

  4. What is half of 250?

    125. Half of 200 is 100 and half of 50 is 25, so 125.

  5. What is 12 × 12?

    144. 144 is called a gross: a dozen dozens.

  6. What is 25% of 80?

    20. 25% is a quarter, so just divide by 4.

  7. What is 9 × 6?

    54. The digits of the first ten multiples of 9 always add up to 9: 5 + 4 = 9.

  8. What is 3 + 4 × 2?

    11. Multiply before you add, so it’s 3 + 8.

  9. How many minutes are there in 3 hours?

    180. 60 × 3 = 180.

  10. What is 1,000 ÷ 8?

    125. Halve it three times: 500, 250, 125.

  11. What is the square root of 81?

    9. 9 × 9 = 81.

  12. What is 15% of 200?

    30. 10% is 20 and 5% is 10, so 15% is 30.

  13. What is 0.5 × 0.5?

    0.25. Half of a half is a quarter.

  14. What is 17 × 6?

    102. 10 × 6 = 60 and 7 × 6 = 42, so 60 + 42 = 102.

  15. What is 45 × 11?

    495. To multiply a two-digit number by 11, add its digits (4 + 5 = 9) and put the answer in the middle: 4-9-5.

  16. Which is bigger: 3/4 or 2/3?

    3/4. As twelfths, 3/4 is 9/12 and 2/3 is 8/12.

  17. What is 999 + 999?

    1,998. Treat it as 1,000 + 1,000, then take away 2.

  18. What is 2 to the power of 10?

    1,024. That’s why computers sometimes count a kilobyte as 1,024 bytes.

  19. How many seconds are there in a day?

    86,400. 60 seconds × 60 minutes × 24 hours = 86,400.

  20. A bat and a ball cost £1.10 in total. The bat costs £1 more than the ball. How much is the ball?

    5p. Most people say 10p, but then the bat would be £1.10 and the total £1.20.