The mean and variance of seven observations are 8 and 16 respectively. If five of the observations are $2,4,10,12,14$, then the product of remaining two observations is

The cumulative distribution function of a discrete random variable X is given by

Then $\mathrm{E(X^2)=}$

If the sum of the deviations of 50 observations from 30 is 50 , then the mean of these observations is

Variance of first n natural numbers is ________.