Quiz Entry - updated: 2026.07.14
Give a quick decision guide: which multiplication trick for which situation?
Pick by the shape of the numbers — a special factor, or closeness to a base.
| The numbers… | Use |
|---|---|
| One factor is 11 | Insert-the-sum (with carry) |
| One factor is 5/25/50/125 | ×(power of ten) then divide |
| One factor is 9/99/999 | ×(round) then subtract |
| One factor halves to something round | Doubling-and-halving |
| Both near 100/1000 | Near-base (Nikhilam) |
| General two-digit × two-digit | Cross method |
All of them are the distributive law in disguise — you're only choosing the easiest split.