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 (4 and
                 repeating 9's)

  1. Choose a number with a 4 and repeating 9's.
  2. The square is made up of:
    • first digits: 24 & one fewer 9 than repeating 9's in the number
    • next digits: same number of 0's as repeating 9's in the number
    • last digit: 1

   Example:

  1. If the number to be squared is 4999:
  2. The square has:

    first digits: 24 and one fewer
      9 than 9's (in the number)      2 4 9 9
    next digits: same number of 0's
      as 9's (in the number)                  0 0 0
    last digit: 1                                    1

  3. So 4999 x 4999 = 24,990,001.

   See the pattern?

  1. If the number to be squared is 499999:
  2. The square has:

    first digits: 24 and one
      fewer 9 than 9's          2 4 9 9 9 9
    next digits: same number
      of 0's as 9's                        0 0 0 0 0
    last digit: 1                                    1

  3. So 499999 x 499999 = 249,999,000,001.
     


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1 March 1999
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