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Multiply by 9 with your fingers

Hold up both hands. Fold one finger. Read the answer. That is the whole trick for 1 to 10, and there is a second trick below for bigger numbers. 手指算九的乘法：弯下一根手指，左边是十位，右边是个位。

Try it nowBigger numbers

Fold a finger

Number your fingers 1 to 10 from left to right. To work out a number times 9, fold that finger down. The fingers on the left of the fold are the tens, the fingers on the right are the ones.

Example: 4 × 9 → fold finger 4. That leaves 3 fingers on the left and 6 on the right, so 4 × 9 = 36.
Two hands with fingers numbered 1 to 10; the chosen finger folds down 1 2 3 4 5 6 7 8 9 10

Fold finger 3. 2 fingers on the left, 7 on the right, so 3 × 9 = 27.

Bigger numbers: times 10, take one away

Fingers run out at 10. For any other number, multiply by 10 first (just add a zero), then subtract the number once. Type each answer and tap Check.

The trick: 23 × 9 → 23 × 10 = 230, then 230 − 23 = 207. Nine is just ten with one taken away. 乘 9 等于乘 10 再减去自己一次。

0 of 6 right so far.

More tricks like this.

Multiply by 11 by splitting the digits, or halve one number and double the other. Printable 10-page packs are $1.99 each on Etsy.

The ×11 trickDouble and halfFull packs on Etsy

For grown-ups: the finger trick works because 9 × n = 10 × (n − 1) + (10 − n). Nothing on this page is saved or sent anywhere; "New numbers" makes a fresh set. Try the Thanksgiving mini-pack for a printable version of the ×11 and double-and-half tricks.