## 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

### Multiply the sum and difference of a 2-                   and a 1-digit number

1. Choose a two-digit multiple of 10 and a single-digit number (1-9).
2. Add the two numbers
3. Find their difference (subtract the smaller from the larger).
4. Multiply the sum and the difference by squaring the two numbers and finding the difference.

#### Example:

1. If the numbers selected are 80 and 3:
2. Add the numbers: 80 + 3 = 83.
3. Subtract 3 from 80: 80 - 3 = 77.
4. 80 × 80 - 3 × 3 = 6400 - 9 = 6391.
5. So 83 × 77 = 6391.

See the pattern?

1. If the numbers selected are 60 and 8:
2. Add the numbers: 60 + 8 = 68.
3. Subtract 8 from 60: 60 - 8 = 52.
4. 60 × 60 - 8 × 8 = 3600 - 64 = 3536.
5. So 68 × 52 = 3536.

Practice and you will be able to multiply sums and differences quickly and accurately.