## 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 297

1. Select a 2-digit number.
2. Multiply by 3.
3. If the product has 2 digits, subtract 1:
X X _ _
Subtract the product from 100: _ _ X X
4. If the product has 3 digits, add 1 to the first digit:
X X X _ _
Subtract this from the product;
Subtract the last 2 digits of the product from 100:
_ _ _ X X

#### Example:

1. The 2-digit number chosen to multiply by 297 is 33.
2. Multiply by 3: 3 × 33 = 99.
3. Subtract 1: 99 - 1 = 98: 9 8 _ _
4. 100 - product: 100 - 99 = 1: _ _ 0 1
5. So 297 × 33 = 9801.

See the pattern?

1. The 2-digit number chosen to multiply by 297 is 92.
2. Multiply by 3: 3 × 92 = 276.
3. Add 1 to the first digit: 2 + 1 = 3
4. Subtract this from the product: 276-3 = 273:
2 7 3 _ _
5. Subtract the last two digits of the product from 100:
100 - 76 = 24: _ _ _ 2 4
6. So 297 × 92 = 27324..