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# $\mu_{2}=20, \mu'_{2}=276$ for a discrete random variable $X$. Then the mean of the random variable $X$ is

$\begin{array}{1 1}(1)16&(2)5\\(3)2&(4)1\end{array}$

$\mu_2 =E(X^2) =[E(X)]^2$------(1)
$\mu_2' =E(X)^2$------(2)
Given $\mu_2=20, \mu_2'=276$
(2) => $E(x^2)=276$
(1) => $20 =276 -[E(X)]^2$
$[E(X)]^2 =276 -20 =256$
$E(X)=\sqrt {256}$
$\qquad=16$
Hence 1 is the correct answer.