Question

The mean of first n natural numbers is equal to (n + 7)/3 then n=?

Answer 1

Mean of  first n natural numbers = (n+7)/3
⇒$\frac{1+2+3+4+.......+n}{n}= \frac{n+7}{3} \\ or, \frac{n}{2n} . [2*1+(n-1).1] = \frac{n+7}{3}$
$\frac{n+1}{2} = \frac{n+7}{3} \\ or,3n+3=2n+14$
or, 3n-2n = 14-3
or,  n = 11