## BEATCALC:  Beat the Calculator!

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 From B. Lee Clay

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### Multiplying a 2-digit number by 86

1. Select a 2-digit number.
2. Multiply it by 9.
3. Add one zero.
4. Subtract four times the original number.

#### Example:

1. The 2-digit number chosen to multiply by 86 is 21.
2. Multiply by 9: 9 × 21 = 189.
3. Add one zero: 1890.
4. Subtract four times the original number: 1890 - 4(21) = 1890 - 84 = 1806.
5. So 86 × 21 = 1806.

See the pattern?

1. Next selection is 52.
2. Multiply by 9: 9 × 52 = 450 + 18 = 468.
3. Add one zero: 4680.
4. Subtract four times the original number: 4680 - 4(52) = 4680 - 208 = 4480 - 8 = 4472.
5. So 86 × 52 = 4472.

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19 December 2007
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