Wednesday, June 20, 2012

Squaring the 2 digit number ending with 5

Let us start with an example: -

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How would you multiply this in conventional way?

Let us solve it: -

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What are the steps you took here?

  • First you multiplied 65 by 5 and wrote it below the line (325)
  • Then you multiplied 65 by 6 and wrote it below the first row leaving one space from right (390)
  • You added the numbers in first row with the numbers in the second row by first putting right most digits down and adding other digits thereafter conventionally.
  • You got 4225 as answer.

Now let us do it by magical method: -

  a5 x  a5 = a(a+1) | 25

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What did we do here?

  • We multiplied 5 by 5 and put 25 as right hand side of the answer.
  • Multiple left digit…i.e. 6 with 6+1 …so we get 6 into 7…so 42

Did you get it?

Let us do some more by the method learned just now!

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