Question

If the mean of the squares of first n natural numbers be 11, then n is equal to ......?

Answer 1

we know, sum of first n natural number is given by Sn = n(n +1)/2

mean = sum of observations/total number of observations
e.g.,mean of first n natural number = Sn/n
11 = n(n +1)/2n
=> 11 = (n + 1)/2
=> n + 1 = 22
=> n = 21

hence, value of n = 21