Find the variance of the following data: $6, 8, 10, 12, 14, 16, 18, 20, 22, 24$

The mean of a set of $10$ observations is $5$ and the standard deviation is $2\sqrt{6}$. If the mean of another set of $20$ observations is $5$ and the standard deviation is $3\sqrt{2}$,what is the standard deviation of the combined set of $30$ observations?

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:

If the standard deviation of the numbers $2, 3, a$,and $11$ is $3.5$,then which of the following is true?

If the variance of $x_1, x_2, \ldots, x_n$ is $\sigma_x^2$,then the variance of $\lambda x_1, \lambda x_2, \ldots, \lambda x_n$ (where $\lambda \neq 0$) is:

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