## BEATCALC:  Beat the Calculator!

Back to Calculation Tips & Tricks

 From B. Lee Clay

Squaring Numbers

Multiplying Numbers

Dividing Numbers

Subtracting Numbers

Finding Percents

Calculation
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### Multiplying a 2-digit number by 8.6

1. Select a 2-digit number.
2. Multiply by 6.
3. Move decimal point one place to the left.
4. To this add eight times original number.

#### Example:

1. The 2-digit number chosen to multiply by 8.6 is 21.
2. Multiply number by 6: 6 × 21 = 126.
3. Move decimal one place to the left: 12.6.
4. To this add eight times the original number: 12.6 + 8(21) = 12.6 + 168 = 178 + 2.6 = 180.6.
5. So 8.6 × 21 is 180.6.

See the pattern?

1. The 2-digit number chosen to multiply by 8.6 is 52.
2. Multiply number by 6: 6 × 52 = 300 + 12 = 312.
3. Move decimal one place to the left: 31.2.
4. To this add eight times the original number: 31.2 + 8(52) = 31.2 + 400 + 16 = 47.2 + 400 = 447.2.
5. So 8.6 × 43 is 447.2.
Remember to add and multiple left to right in manageable parts and you will be able to give these answers quickly and accurately.