## BEATCALC:  Beat the Calculator!

Back to Calculation Tips & Tricks

 From B. Lee Clay

Squaring Numbers

Multiplying Numbers

Dividing Numbers

Adding Numbers

Subtracting Numbers

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### Adding consecutive numbers between two               numbers

Choose two 2-digit numbers less than 20
(no limits for experts).
Add all the numbers between them:
1. Add the numbers;
2. Subtract the numbers and add 1;
3. Multiply half the sum by this difference + 1, OR
Multiply the sum by half the difference + 1.

#### Example:

1. If the two numbers selected are 6 and 19:
2. Add the numbers: 6 + 19 = 25.
3. Subtract the numbers: 19 - 6 = 13. Add 1: 13 + 1 = 14.
4. Multiply 25 by half of 14: 25 × 7 = 175.
5. So the sum of the numbers from 6 through 19 is 175.

See the pattern?

1. If the two numbers selected are 4 and 18:
2. Add the numbers: 4 + 18 = 22.
3. Subtract the numbers: 18 - 4 = 14. Add 1: 14 + 1 = 15.
4. Multiply half of 22 by 15: 11 × 15 = 165 (10 × 15 + 15).
5. So the sum of the numbers from 4 through 18 is 165.

Practice with examples restricted to less than 20, then advance to larger numbers. You will impress your friends when you beat the calculator.

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