## BEATCALC:  Beat the Calculator!

Back to Calculation Tips & Tricks

 From B. Lee Clay

Squaring Numbers

Multiplying Numbers

Dividing Numbers

Adding Numbers

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### Multiplying a 2-digit number by 5.6

1. Multiply the number by 6.
2. Move decimal point one place to the left.
3. Add to 5 times the original number.

#### Example:

1. The first number to multiply by 5.6 is 21.
2. Multiply by 6: 6 × 21 = 126.
3. Move decimal point one place to the left: 12.6.
4. Add this to 5 times the original number: 12.6 + 5(21) = 12.6 + 100 + 5 = 17.6 + 100 = 117.6.
5. So 5.6 × 21 = 117.6.

See the pattern?

1. The second number to multiply by 5.6 is 35.
2. Multiply by 6: 6 × 35 = 180 + 30 = 210.
3. Move decimal one place to the left: 21.0.
4. Add this to 5 times the original number: 21 + 5(35) = 21 + 150 + 25 = 46 + 150 = 196.
5. So 5.6 × 35 is 196.

With these steps you will be able give correct answers using mental math. And beat the friend using a calculator.

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