## 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 two 2-digit numbers(difference of 8)

1. Choose a 2-digit number.
2. Select a number either 8 smaller or 8 larger.
3. Find the middle number of the two (the average).
4. Square this middle number (multiply it by itself).
5. Subtract 16 from this square.

#### Example:

1. If the first number is 34, choose 26 as the second number (8 smaller).
2. The middle number (the average) is 30.
3. Square this middle number: 30 × 30 = 900.
4. Subtract 16 from this square: 900 - 16 = 884.
5. So 34 × 26 = 884.

See the pattern?

1. If the first number is 64, choose 72 as the second number (8 larger).
2. The middle number (the average) is 68.
3. Square this middle number: 68 × 68 = 4624. (Remember how to square a 2-digit number ending in 8?)
4. Subtract 16 from this square: 4624 - 16 = 4608.
5. So 64 × 72 = 4608.

Choose the second number that will give you the easier square, and use your square shortcuts. Practice!