If $1$ is added to each of the first $10$ natural numbers,then the variance of the numbers so obtained is:

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

If the coefficient of variation and variance of a frequency distribution are $7.2$ and $3.24$ respectively,then its mean is

Find the variance of the first $n$ natural numbers.

In a discrete data,$\frac{1}{4}$ of the observations are equal to $a$,another $\frac{1}{4}$ of the observations are equal to $-a$. Out of the remaining,half of them are equal to $b$ and the rest are equal to $-b$. If the variance of all the observations is $ab$,then:

In a series of $2n$ observations,half of them are equal to $a$ and the remaining half are equal to $-a$. If the standard deviation of these observations is $2$,then $|a|$ equals: