Question

If the mean deviation about the mean of the numbers $1,2,3,\dots .,n$, where $n$ is odd, is $\frac{5(n+1)}{n}$, then $n$ is equal to_____

Answer 1

Answer: 21

Mcan deviation about mean of first $n$ natural numbers is $\frac{n^2-1}{4n}$
$\therefore n=21$