MCQ
The p.m.f. of a random variable $X$ is
$
P(x)=\left\{\begin{array}{cc}
\frac{2 x}{n(n+1)}, & x=1,2,3, \ldots . . n \\
0, & \text { otherwise, }
\end{array}\right.
$
then $E(X)$ is
$
P(x)=\left\{\begin{array}{cc}
\frac{2 x}{n(n+1)}, & x=1,2,3, \ldots . . n \\
0, & \text { otherwise, }
\end{array}\right.
$
then $E(X)$ is
- A$\frac{n+1}{6}$
- B$\frac{2 n+1}{6}$
- C$\frac{n+1}{3}$
- D$\frac{2 n+1}{3}$