BEATCALC:  Beat the Calculator!

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Back to Calculation Tips & Tricks
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From the BEATCALC mailing list:
a weekly service from B. Lee Clay, archived here by the Math Forum.
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   Multiplying a repeating 3-digit number by 2,
                   then dividing by 37

  1. Choose a repeating 3-digit number (one whose numbers are all the same).
  2. Add its digits (or multiply one of them by 3).
  3. Multiply by 2.

   Example:

  1. If the first number is 555:
  2. Add its digits (or multiply 5 x 3) = 15.
  3. Multiply 15 x 2 = 30.
  4. So 555 x 2 / 37 = 30.

   See the pattern?

  1. If the first number is 888:
  2. Add 8 + 8 + 8 or multiply 8 x 3 = 24.
  3. Multiply 24 x 2 = 48.
  4. So 888 x 2 / 37 = 48.


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