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rev 4 · 2026-07-15

The 9×9 table, and the trick for the tough corner

Green cells (6–9 × 6–9) are the hard ones. Tap any cell to see the technique animated.

Finger / complement trick zone Easy — area model ⤢ dashed = squares

Tap 7 × 8 to start with the classic example.

The trick, drawn by hand — the folded orange fingers add to the tens, the raised blue fingers multiply to the units:

7 × 7 = 49 on fingers: four folded orange fingers make 40, and a 3×3 blue grid makes 9
7 × 7 = 49. The folded orange fingers add up to the tens — 2 + 2 = 4 → 40; the raised blue grid is 3 × 3 = 9 units.
7 × 8 = 56 on fingers: five folded orange fingers make 50, and a 3×2 blue grid makes 6
7 × 8 = 56. The folded orange fingers add up to the tens — 2 + 3 = 5 → 50; the raised blue grid is 3 × 2 = 6 units.