## 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 a 2-digit number by 9.7

1. Select a 2-digit number.
2. Multiply by 3.
3. Move decimal point one place left.
4. Subtract this from ten times the original number.

#### Example:

1. The 2-digit number chosen to multiply by 9.7 is 21.
2. Multiply by 3: 3 × 21 = 63
3. Move decimal one place left: 6.3
4. Subtract this from ten times the original number: 210 - 6.3 = 204 - 0.3 = 203.7
5. So 9.7 × 21 is 203.7.

See the pattern?

1. The 2-digit number chosen to multiply by 9.7 is 37.
2. Multiply by 3: 3 × 37 = 90 + 21 = 111
3. Move decimal one place left: 11.1
4. Subtract this from ten times original number: 370 - 11.1 = 360 - 1.1 = 359 - .1 = 358.9
5. So 9.7 × 37 is 358.9.
Practice subtracting left to right in small increments and you will be giving these answers quickly.