## 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

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### Multiplying a repeating 1's number by 19

1. Choose a repeating 1's number (111, 1111, etc.)
2. Multiply it by 19
3. The product is:
- the first digit is 2
- the next digits are repeating 1's (two fewer than repeating 1's in the original number)
- the final two digits are 09

#### Example:

1. If the first number is 1111:
2. First digit is 2.
3. Next digits are repeating 1's -- two fewer than repeating 1's in the original number: 11.
4. Last two digits are 09.
5. So 19 × 1111 = 21109.

See the pattern?

1. Next pick is 1111111:
2. First digit is 2.
3. Next digits are repeating 1's -- two fewer than repeating 1's in the original number: 11111.
4. Last two digits are 09.
5. So 19 × 1111111 = 21111109.

Remember these three steps and you will be able to give these products quickly and easily.