## BEATCALC:  Beat the Calculator!

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 From B. Lee Clay

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### Multiplying a 2-digit number by 5 1/2

1. Select a 2-digit number.
2. Multiply by 11 (add digits from right to left; see examples).
3. Divide the product by 2.

#### Example:

1. The 2-digit number chosen to multiply by 5 1/2 is 24.
2. Multiply by 11: the right digit is 4, the middle digit is 4 + 2 = 6, and the left digit is 2: 264
3. Divide by 2: 264/2 = 132
4. So 24 × 5 1/2 = 234.

See the pattern?

1. The 2-digit number chosen to multiply by 5 1/2 is 38.
2. Multiply by 11: : the right digit is 8, the middle digit is 8 + 3 = 11 (carry 1), and the left digit is 3 + 1 = 4: 418
3. Divide by 2: 418/2 = 209
4. So 38 × 5 1/2 = 209.
To give these products quickly and accurately, review multiplying by 11.

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26 February 2001
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