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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   Squaring numbers in the hundreds

  1. Choose a number over 100 (keep it low for practice,
    then go higher when expert).
  2. The last two places will be the square of
    the last two digits (keep any carry) _ _ _ X X.
  3. The first three places will be the number plus
    the last two digits plus any carry: X X X _ _.

   Example:

  1. If the number to be squared is 106:
  2. Square the last two digits (no carry): 6 x 6 = 36: _ _ _ 3 6
  3. Add the last two digits (06) to the number: 106 + 6 = 112: 1 1 2 _ _
  4. So 106 x 106 = 11236.

   See the pattern?

  1. If the number to be squared is 112:
  2. Square the last two digits (keep carry 1): 12 x 12 = 144: _ _ _ 4 4
  3. Add the last two digits (12) plus the carry (1) to the number:
    112 + 12 + 1 = 125: 1 2 5 _ _
  4. So 112 x 112 = 12544.

With a little practice your only limit will be your ability to square the last two digits!


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27 May 1996
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