## 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 495

1. Select a 2-digit number .
2. Multiply by 5.
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 _ _ (don't add 1 if the last two digits are zeros)
Subtract this from the product: X X X _ _
Subtract the last 2 digits of the product from 100:
_ _ _ X X

#### Example:

1. The 2-digit number chosen to multiply by 495 is 18.
2. Multiply by 5: 5 × 18 = 90.
3. Subtract 1: 90 - 1 = 89: 8 9 _ _
4. 100 - product: 100 - 90 = 10: _ _ 1 0
5. So 495 × 18 = 8910.

See the pattern?

1. The 2-digit number chosen to multiply by 495 is 67.
2. Multiply by 5: 5 × 67 = 300 + 35 = 335.
3. Add 1 to the first digit: 3 + 1 = 4
4. Subtract this from the product: 335-4 = 331:
3 3 1 _ _
5. Subtract the last two digits of the product from 100:
100 - 35 = 65: _ _ _ 6 5
6. So 495 × 67 = 33165.