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 1 3/4

  1. Multiply the number by 7.
  2. Divide by 4.

   Example:

  1. If the number chosen to multiply by 1 3/4 is 42:
  2. Multiply by 7: 7 x 42 = 280 + 14 = 294
  3. Divide by 4: 294/4 = 73 2/4
  4. So 42 x 1 3/4 = 73 1/2.

   See the pattern?

  1. If the number to be multiplied by 1 3/4 is 29:
  2. Multiply by 7: 7 x 29 = 140 + 63 = 203
  3. Divide by 4: 203/4 = 50 3/4
  4. So 29 x 1 3/4 = 50 3/4.

      Practice, and these products will be fast and accurate.


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28 December 1998
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