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 (9's and final 3)

  1. Choose a number with repeating 9's and a final 3.
  2. The square is made up of:
    • one fewer 9 than there are repeating 9's
    • 86
    • the same number of 0's as there are 9's in the square
    • A final 49

   Example:

  1. If the number to be squared is 9993:
  2. The square has:

    one fewer 9 than the
       repeating 9's:         9 9
    86                            8 6
    same number of 0's as 9's
       in the square                  0 0
    a final 49                            4 9

  3. So 9993 x 9993 = 99860049.

   See the pattern?

  1. If the number to be squared is 999993:
  2. The square has:

    one fewer 9 than the
       repeating 9's:      9 9 9 9
    86                             8 6
    same number of 0's as 9's
       in the square                   0 0 0 0
    a final 49                                 4 9

  3. So 999993 x 999993 = 999986000049.

Using this pattern you will be able to square these large numbers with ease.


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26 April 1999
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