If a possion variate $X$ satisfies the relation $P(X=3)=P(X=5)$, then $P(X=4)=$

If the variance of the numbers $9,15,21, \ldots,(6 n+3)$ is $P$, then the variance of the first $n$ even numbers is

The mean deviation from the median for the following data is

$$ \begin{array}{cllllll} x_i & 2 & 9 & 8 & 3 & 5 & 7 \\ \hline f_i & 5 & 3 & 1 & 6 & 6 & 1 \\ \hline \end{array} $$

If three dice are thrown, then the mean of the sum of the numbers appearing on them is