## 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 1.9

1. Select a 2-digit number.
2. Multiply the number by 9.
3. Move the decimal point one place left.
4. Add this to the original number.

#### Example:

1. The 2-digit number chosen to multiply by 1.9 is 21.
2. Multiply by 9: 9 × 21 = 189.
3. Move decimal one place left: 18.9.
4. Add original number: 18.9 + 21 = 39.9.
5. So 1.9 × 21 = 39.9.

See the pattern?

1. The 2-digit number chosen to multiply by 1.9 is 33.
2. Multiply by 9: 9 × 33 = 270 + 27 = 297.
3. Move decimal on place left: 29.7.
4. Add original number: 29.7 + 33 = 59.7 + 3 = 62.7.
5. So 1.9 × 33 = 62.7.

Alternate method: Subtract .1 of original number (move decimal one place left) from 2 times original number. Try this method, too.

With some practice you will be able to give these products using one or both of these methods.