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 4 1/2

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

   Example:

  1. The 2-digit number chosen to multiply by 4 1/2 is 52.
  2. Multiply by 9: 52 x 9 = 450 +18 = 468
  3. Divide by 2: 468/2 = 234
  4. So 52 x 4 1/2 = 234.

   See the pattern?

  1. The 2-digit number chosen to multiply by 4 1/2 is 91.
  2. Multiply by 9: 91 x 9 = 810 + 9 = 819
  3. Divide by 2: 819/2 = 409 1/2
  4. So 91 x 4 1/2 = 409 1/2.


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6 December 1999
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