Double and halve
Halve one number and double the other until it gets easy. 16 × 25 = 8 × 50 = 400.
How long?
Type the answer. Correct answers move on by themselves. Press Enter to skip a wrong one.
How the trick works
- Find an even number to halve.
- Double the other number.
- Repeat until the multiplication is easy.
Worked examples
16 × 25: halve 16 and double 25.
8 × 50 = 400.
14 × 15: halve 14 and double 15.
7 × 30 = 210.
18 × 35: halve 18 and double 35.
9 × 70 = 630.
Practise it
Take the 1 minute drill above a few times. When you can do most of them without slowing down, try level 4, which mixes this trick with others.