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 2-digit number by 2 1/4

  1. Select a 2-digit number.
  2. Multiply the number by 9.
  3. Divide by 4.

   Example:

  1. The 2-digit number chosen to multiply by 2 1/4 is 51.
  2. Multiply by 9: 9 x 51 = 450 + 9 = 459.
  3. Divide by 4: 459/4 = 114 3/4.
  4. So 51 x 2 1/4 = 114 3/4.

   See the pattern?

  1. The 2-digit number chosen to multiply by 2 1/3 is 28.
  2. Multiply by 9: 9 x 28 = 180 + 72 = 252.
  3. Divide by 4: 252/4 = 63.
  4. So 51 x 2 1/4 = 63.


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22 November 1999
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