The standard deviation of the data $6, 7, 8, 9, 10$ is

If the sum of $10$ observations and the sum of their squares are $12$ and $18$ respectively,then the standard deviation of the observations is:

The standard deviation of $a, a+d, a+2 d, \ldots, a+2 n d$ is

If $\sum_{i=1}^{n}(x_{i}-a)=n$ and $\sum_{i=1}^{n}(x_{i}-a)^{2}=na$,where $n, a > 1$,then the standard deviation of $n$ observations $x_{1}, x_{2}, \ldots, x_{n}$ is

The mean and variance of a series of $5$ observations are $8$ and $24$ respectively. The mean and variance of another series of $3$ observations are $8$ and $24$ respectively. What is the variance of their combined series?

The standard deviation of $25$ numbers is $40$. If each of the numbers is increased by $5$,then the new standard deviation will be