Probability

The p.m.f of random variate \(\mathrm{X}\) is $$P(X)= \begin{cases}\frac{2 x}{\mathrm{n}(\mathrm{n}+1)}, & x=1,2,3, \ldots \ldots, \mathrm{n} \\ 0, & \text { otherwise }\end{cases}$$

Then \(\mathrm{E}(\mathrm{X})=\)