## BEATCALC:  Beat the Calculator!

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 From B. Lee Clay

Squaring Numbers

Multiplying Numbers

Dividing Numbers

Subtracting Numbers

Finding Percents

Calculation
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### Multiplying two selected 3-digit numbers(middle digit 5)

1. Select a 3-digit number with a middle digit of 5 (last digit not zero).
2. Choose a multiplier with the same first two digits, whose third digit sums to 10 with the third digit of the first 3-digit number.
3. The last three digits will be 0 and the product of the third digits: _ _ _ 0 X X.
4. The third digit from the right will be the first digit + 3 (keep the carry): _ _ X _ _.
5. The first digit will be the first digit times the next number plus the carry: X X _ _ _ _.

Repeat those digits from left to right as you get them.

#### Example:

1. If the first number is 752, choose 758 as the second number (same first digits, third digits add to 10).
2. Last three digits: 0 and the product of the third digits:
2 × 8 = 16: _ _ 0 1 6
3. Next digit: first digit + 3: 7 + 3 = 10 (keep carry 1):
_ _ 0 _ _ _
4. First two digits: first digit times next number plus carry: 7 × 8 = 56, 56 + 1 = 57: 5 7 _ _ _ _
5. So 752 × 758 = 570016.

See the pattern?

1. If the first number is 654, choose 656 as the second number (same first digits, third digits add to 10).
2. Last three digits: 0 and the product of the third digits:
4 × 6 = 24: _ _ 0 2 4
3. Next digit: first digit + 3: 6 + 3 = 9: _ _ 9 _ _ _
4. First two digits: first digit times next number:
6 × 7 = 42: 4 2 _ _ _ _
5. So 654 × 656 = 429024.