## 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 a 2-digit number by 4.6

1. Multiply the number by 6.
2. Move decimal point one place to the left.
3. Add to 4 times the original number.

#### Example:

1. The first number to multiply by 4.6 is 21.
2. Multiply by 6: 6 × 21 = 126.
3. Move decimal point one place to the left: 12.6.
4. Add this to 4 times the original number: 12.6 + 4(21) = 12.6 + 84 = 96 + .6 = 96.6.
5. So 4.6 × 21 = 96.6.

See the pattern?

1. The second number to multiply by 4.6 is 73.
2. Multiply by 6: 6 × 73 = 420 + 18 = 438.
3. Move decimal one place to the left: 43.8.
4. Add this to 4 times the original number: 43.8 + 4(73) = 43.8 + 280 + 12 = 55.8 + 280 = 330 + 5.8 = 335.8.
5. So 4.6 × 73 is 335.8.

Multiply and add left to right and you will be able to do these computations using mental math.