Question

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

Answer 1

The correct answer is: 21

Mean

$=\frac{\frac{n(n+1)}{2}}{n}=\frac{n+1}{2}$

$⇒((n-1)+(n-3)+(n-5)+...0=5)=5(n+1)$

$⇒(\frac{n+1}{4})(n-1)=5(n+1)$

So, n = 21.