## 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

Full List

### Multiplying two selected 3-digit numbers(middle digit 4)

1. Select a 3-digit number with a middle digit of 4 (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 9 times the first digit + 2 (keep the carry): _ _ X _ _.
5. The first two digits will be the square of the first digit plus the carry: X X _ _ _ _.

As you determine the digits in the answer from right to left, repeat them to yourself at each step until you have the whole answer.

#### Example:

1. If the first number is 541, choose 549 as the second number (same first digits, third digits add to 10).
2. Last three digits: 0 and the product of the third digits: 1 × 9 = 9: _ _ 0 0 9
3. Next digit: 9 times the first digit + 2: 9 × 5 = 45, 45 + 2 = 47 (keep carry 4): _ _ 7 _ _ _
4. First two digits: square the first and carry: 5 × 5 = 25, 25 + 4 = 29: 2 9 _ _ _ _
5. So 541 × 549 = 297009.

See the pattern?

1. If the first number is 344, choose 346 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: 9 times the first digit + 2: 9 × 3 = 27, 27 + 2 = 29 (keep carry 2): _ _ 9 _ _ _
4. First two digits: square the first and carry: 3 × 3 = 9, 9 + 2 = 11: 1 1 _ _ _ _
5. So 344 × 346 = 119024.