Percentages in your head
10% moves the point, 5% is half of that, 20% is double. Handy for tips and discounts.
How long?
Type the answer. Correct answers move on by themselves. Press Enter to skip a wrong one.
How the trick works
- Find 10% by moving the decimal point one place left.
- Halve it for 5%, double it for 20%.
- Add 10% and 5% to get 15%.
Worked examples
10% of 340: move the decimal point one place left.
340 becomes 34.
15% of 80: 10% is 8 and 5% is 4.
Add them: 12.
20% of 65: find 10% first, 6.5.
Double it: 13.
Practise it
Take the 1 minute drill above a few times. When you can do most of them without slowing down, try level 5, which mixes this trick with others.