## 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 4-digit number by 137, then                   by 73; subtract 1200

1. Choose a 4-digit number (one whose numbers are all the same).
2. Multiply by 137 and multiply the product by 73.
3. The second product is an 8-digit number: the original number and a repeat of the digits.
4. Subtract 1200.

#### Example:

1. If the first number is 6241:
2. The answer to the two multiplications is 62416241
3. Subtract 1200: 62416241 - 1200 = 62415041
4. So 6241 × 137 × 73 = 62,415,041.

See the pattern?

1. If the first number is 7834:
2. The answer to the two multiplications is 78347834
3. Subtract 1200: 78347834 - 1200 = 78346634
4. So 7834 × 137 × 73 = 78,346,634.

You can expand this exercise by changing the final step to another calculation: add or subtract a number that is easy to handle. In this way you can create many new exercises.