Quiz Entry - updated: 2026.07.14
Which squaring shortcut fits which number — a quick guide?
Match by the number's neighbourhood; fall back to the cross method for anything else.
| The number… | Fastest method |
|---|---|
| Ends in 5 | n(n+1) then "25" |
| Near 50 | 25 ± d, then d² |
| Near 100 (or 1000) | number ± d, then d² |
| Near a multiple of 10 | (a ± b)² identity |
| None of the above | Cross method (a² | 2ab | b²) |
All five are the same algebra — a binomial square — with a chosen to make the arithmetic land on round numbers.