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 2/9

  1. Select a 2-digit number.
  2. Multiply by two.
  3. Add one zero.
  4. Divide by nine.

   Example:

  1. The 2-digit number chosen to multiply by 2 2/9 is 31.
  2. Multiply by 2: 2 x 31 = 62
  3. Add one zero: 620
  4. Divide by 9: 620/9 = 68 8/9
  5. So 31 x 2 2/9 = 68 8/9.

   See the pattern?

  1. The 2-digit number chosen to multiply by 2 2/9 is 74.
  2. Multiply by 2: 2 x 74 = 148
  3. Add one zero: 1480
  4. Divide by 9: 1480/9 = 164 4/9
  5. So 74 x 2 2/9 = 164 4/9.
Those using calculators will have difficulty entering 2 2/9 (2.222222...) and their results may be repeating decimals. Your steps will produce exact results.


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7 August 2000
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