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 special numbers (1 and
                 repeating 9's)

  1. Choose a number with a 1 and repeating 9's.
  2. The square is made up of:
    • first digits: 3 & one fewer 9 than repeating 9's
    • next digits: 6 & one fewer 0 than repeating 9's
    • last digit: 1

   Example:

  1. If the number to be squared is 1999:
  2. The square has:

    first digits: 3 and one fewer
        9 than 9's                      3 9 9
    next digits: 6 and one fewer
        0 than 9's                            6 0 0
    last digit: 1                                   1

  3. So 1999 x 1999 = 3996001.

   See the pattern?

  1. If the number to be squared is 199999:
  2. The square has:

    first digits: 3 and one fewer
       9 than 9's                 3 9 9 9 9
    next digits: 6 and one fewer
        0 than 9's      &                   6 0 0 0 0
    last digit: 1                                     1

  3. So 199999 x 199999 = 39999600001.
     


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1 February 1999
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