## BEATCALC:  Beat the Calculator!

Back to Calculation Tips & Tricks

 From B. Lee Clay

Squaring Numbers

Multiplying Numbers

Dividing Numbers

Subtracting Numbers

Finding Percents

Calculation
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### Multiplying a 2-digit number by 7.4

1. Select a 2-digit number.
2. Multiply number by 4.
3. Move decimal point one place to the left.
4. Add this to 7 times original number.

#### Example:

1. The 2-digit number chosen to multiply by 7.4 is 21.
2. Multiply number by 4: 4 × 21 = 84.
3. Move decimal one place to the left: 8.4.
4. Add to original number: 8.4 + 7(21) = 8.4 + 140 + 7 = 8.4 + 147 = 155.4.
5. So 7.4 × 21 is 155.4.

See the pattern?

1. The 2-digit number chosen to multiply by 7.4 is 46.
2. Multiply number by 4: 4 × 46 = 160 + 24 = 184.
3. Move decimal one place to the left: 18.4.
4. Add seven times original number: 18.4 + 7(46) = 18.4 + 280 + 42 = 60.4 + 280 = 340 + 0.4 = 340.4.
5. So 7.4 × 46 is 340.4.
Remember to add and multiply left to right in small increments easy to handle and you will be giving these products easily.