## 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 5.2

1. Select a 2-digit number.
2. Multiply the number by 2.
3. Move decimal point one place to the left.
4. Add this to 5 times original number.

#### Example:

1. The 2-digit number chosen to multiply by 5.2 is 21.
2. Multiply the number by 2: 2 × 21 = 42.
3. Move decimal one place to the left: 4.2.
4. Add to 5 times original number: 4.2 + 5(21) = 4.2 + 105 = 109.2.
5. So 5.2 × 21 is 109.2.

See the pattern?

1. The 2-digit number chosen to multiply by 5.2 is 72.
2. Multiply the number by 2: 2 × 72 = 144.
3. Move decimal one place to the left: 14.4.
4. Add to 5 times original number: 14.4 + 5(72) = 14.4 + 350 + 10 = 24.4 + 350 = 374.4.
5. So 5.2 × 72 is 374.4.
Remember to multiply and add left to right and these answers will come easily.