The variance of $20$ observations is $5$. If each observation is multiplied by $2$,find the new variance of the resulting observations.

If the variance of the following frequency distribution is $50$,then $x$ is equal to:

Class	$10-20, 20-30, 30-40$
Frequency	$2, x, 2$

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

Let $x_1, x_2, \dots, x_{100}$ be $100$ observations such that $\sum x_i = 0$,$\sum_{1 \le i < j \le 100} |x_i x_j| = 80000$,and the mean deviation from their mean is $5$. Then their standard deviation is:

The mean and standard deviation of marks obtained by $50$ students of a class in three subjects,Mathematics,Physics and Chemistry are given below:

Subject	Mathematics,Physics,Chemistry
Mean	$42, 32, 40.9$
Standard deviation	$12, 15, 20$

Which of the three subjects shows the highest variability in marks and which shows the lowest?

The coefficient of variation of the following distribution is

Class interval	$0-5$	$5-10$	$10-15$	$15-20$	$20-25$
Frequency	$4$	$1$	$10$	$3$	$2$