← Methods
Multiply by 9
Nine of something is ten of it less one of it. Shift it up to ten times, then take the original back off.
When it works
Anything times 9 — and it keeps working long after the times table runs out.
Worked through
27 × 9 = 243
- 27 × 10 = 270Ten times anything is a shift, so start there.
- 270 − 27 = 243Nine of them is ten of them less one.
10 problems, every one of them this method.