## BEATCALC:  Beat the Calculator!

Back to Calculation Tips & Tricks

 From B. Lee Clay

Squaring Numbers

Multiplying Numbers

Dividing Numbers

Subtracting Numbers

Finding Percents

Calculation
Practice Exercises

Full List

### Multiplying a repeating 9's number by 25

1. Choose a repeating 9's number (999, etc.)
2. Multiply it by 25
3. The product is:
- first two digits are 24
- next repeating digits are 9's, two fewer than
repeating 9's in the original number
- the last two digits are 75

#### Example:

1. If the first number is 99999:
2. Multiply by 25. The product is:
- first two digits are 24: 24.
- next repeating digits are 9's, two fewer than
repeating 9's in the original number: 999.
- the last two digits are 75: 75.
3. So 99999 × 25 = 2499975.

See the pattern?

1. If the first number is 9999999999:
2. Multiply by 25. The product is:
- first two digits are 24: 24.
- next repeating digits are 9's, two fewer than
repeating 9's in the original number: 99999999.
- the last two digits are 75: 75.
3. So 99999 × 25 = 249999999975.
Using the three steps you will be able to give these big products with ease. What will your friend with the calculator do?