## BEATCALC:  Beat the Calculator!

Back to Calculation Tips & Tricks

 From B. Lee Clay

Squaring Numbers

Multiplying Numbers

Dividing Numbers

Subtracting Numbers

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Calculation
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### Multiplying a 2-digit number by 1 4/7

1. Multiply the number by 11. (See procedure below.)
2. Divide the product by 7.

#### Example:

1. If the 2-digit number chosen to multiply by 1 4/7 is 21:
2. Multiply by 11:
The right digit is 1 (same as number): 1
The middle digit is the sum of the two digits of the number: 2 + 1 = 3
The left digit is the left digit of the number: 2
So 11 × 21 = 231
3. Divide by 7: 231/7 = 33
4. So 1 4/7 × 21 = 33.

See the pattern?

1. If the 2-digit number chosen to multiply by 1 4/7 is 52:
2. Multiply by 11:
The right digit is 1 (same as number): 1
The middle digit is the sum of the two digits of the number: 5 + 2 = 7
The left digit is the left digit of the number: 5 So 11 × 52 = 572
3. Divide by 7: 572/7 = 81 5/7
4. So 1 4/7 × 52 = 81 5/7.
Practice multiplying by 11 and you will be proficient in giving these products.