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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  Finding 45 percent of a number

  1. Choose a 2-digit number.
  2. Multiply the number by 9.
  3. Divide by 2.
  4. Move the decimal point one place to the left.

   Example:

  1. If the number selected is 36:
  2. Multiply by 9: 9 x 36 = 270 + 54 = 324
  3. Divide by 2: 324/2 = 163
  4. Move the decimal point one place to the left: 16.2
  5. So 45% of 36 = 16.2.

   See the pattern?

  1. If the number selected is 52:
  2. Multiply by 9: 9 x 52 = 450 + 18 = 468
  3. Divide by 2: 468/2 = 234
  4. Move the decimal point one place to the left: 23.4
  5. So 45% of 52 = 23.4.


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3 January 2000
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