## 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 two 2-digit numbers(difference of 3)

1. Choose a 2-digit number.
2. Select a number either 3 smaller or 3 larger.
3. Add 1 to the smaller number, then square.
4. Subtract one from the smaller number.
5. Add this to the square.

#### Example:

1. If the first number is 27, choose 24 as the second number.
2. Add 1 to the smaller number: 24 + 1 = 25.
3. Square this number: 25 × 25 = 625.
4. Subtract one from the smaller number: 24 - 1 = 23.
5. Add this to the square: 625 + 23 = 648.
6. So 27 × 24 = 648.

See the pattern?

1. If the first number is 34, choose 31 as the second number.
2. Add 1 to the smaller number: 31 + 1 = 32.
3. Square this number: 32 × 32 = 1024.
4. Subtract one from the smaller number: 31 - 1 = 30.
5. Add this to the square: 1024 + 30 = 1054.
6. So 34 × 31 = 1054.

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