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Question:
if n is the smallest natural no. such that n+2n+3n+....+99n is a perfect square,then the no. of digits in square of n is
Answer:

Given that  

       n+2n+3n+....+99n

   = n*(1+2+3+........+99)

   = (n*99*100)/2

   = n*99*50

   = n*9*11*2*25

To make it perfect square we need 2*11

So n = 2*11 = 22

Now n2 = 22*22 = 484

So number of digit in n2 = 3

 

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