## 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 repeating 1's number by 18

1. Choose a repeating 1's number (111, etc.)
2. Multiply it by 18
3. The product is:
- first digit is 1
- next digits are 9's - one fewer than repeating 1's in the original number
- last digit is 8.

#### Example:

1. If the first number is 11111:
2. Multiply by 18. The product is:
first digit is 1: 1
next digits are 9's, one fewer than 1's: 88888
last digit is 8: 8
3. So 11111 × 18 = 199998.

See the pattern?

1. If the first number is 111111111:
2. Multiply by 18. The product is:
first digit is 1: 1
next digits are 9's, one fewer than 1's: B 99999999
last digit is 8: 8
3. So 1111111111 × 18 = 1999999998.
Follow these three steps and you will be able to give these sometimes large products with ease. Your friend's calculator will not be able to handle these large ones.