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 50s

  1. Square the last digit (keep the carry)   _ _ _ X
  2. Multiply the last digit by 10, add the carry   _ _ X _
  3. The first digits will be 25 plus the carry:   X X _ _

   Example:

     If the number to be squared is 53:

  1. Square the last digit (keep the carry):
        3 x 3 = 9 (keep 3)     _ _ _ 9
  2. Multiply the last digit by 10, add the carry:
        10 x 3 = 30 (keep 3)    _ _ 0 _
  3. The first digits will be 25 plus the carry:
        25 (+ carry): 25 + 3 = 28    2 8 _ _
  4. So 53 x 53 = 2809.

   See the pattern?

     If the number to be squared is 56:

  1. Square the last digit (keep the carry):
        6 x 6 = 36 (keep 3)     _ _ _ 6
  2. Multiply the last digit by 10, add the carry:
        10 x 6 = 60, 60 + 3 = 63    _ _ 3 _
  3. The first digits will be 25 plus the carry:
        25 (+ carry): 25 + 6 = 31  3 1 _ _
  4. So 53 x 53 = 3136.

Practice and you will soon be producing these products quickly and accurately.


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13 July 1998
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