## BEATCALC:  Beat the Calculator!

Back to Calculation Tips & Tricks

 From B. Lee Clay

Squaring Numbers

Multiplying Numbers

Dividing Numbers

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### Multiplying a repeating 5's number by 28

1. Choose a repeating 5's number (555, etc.)
2. Multiply it by 28
3. The product is:
- the first two digits are 15
- the next digits are repeating 2's (two fewer than repeating 2's in the original number)
- the last two digits are 40

#### Example:

1. The number chosen to multiply by 28 is 55555.
2. Multiply by 28. The product is:
- the first two digits are 15
- the next digits are repeating 2's (two fewer than repeating 2's in the original number): 555.
- the last two digits are 40: 40.
3. So 28 × 55555 is 1555540.

See the pattern?

1. The number chosen to multiply by 28 is 555555555.
2. Multiply by 28. The product is:
- the first two digits are 15: 15.
- the next digits are repeating 2's (two fewer than repeating 2's in the original number): 5555555.
- the last two digits are 40: 40.
3. So 28 × 555555555 is 15555555540.