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 375

  1. Select a 2-digit number.
  2. Multiply by 3.
  3. Divide by 8.
  4. Move the decimal point 3 places to the right.

   Example:

  1. The 2-digit number chosen to multiply by 375 is 38.
  2. Multiply by 3: 3 x 38 = 90 + 24 = 114
  3. Divide by 8: 114/8 = 14 2/8 14.25
  4. Move the decimal point 3 places to the right: 14250
  5. So 375 x 38 = 14250.

   See the pattern?

  1. The 2-digit number chosen to multiply by 375 is 64.
  2. Multiply by 3: 3 x 64 = 180 + 12 = 192
  3. Divide by 8: 192/8 = 24
  4. Move the decimal point 3 places to the right: 24000
  5. So 375 x 64 = 24000.

Multiply left to right to get products, and express the remainder as a fraction that is easily written as a decimal.


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10 August 1998
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