The mean and standard deviation of $100$ items are $50$ and $4$ respectively. The sum of the squares of all the items is:

If the variance of the numbers $-1, 0, 1, k$ is $5$,where $k > 0$,then $k$ is equal to

Find the coefficient of variation for the given observations: $10, 14, 11, 9, 8, 12, 6$. (in $\%$)

Variance of first $n$ natural numbers is $\qquad$ .

The standard deviation of $n$ observations $a_{1}, a_{2}, a_{3}, \ldots, a_{n}$ is $\sigma$. Then, the standard deviation of the observations $\lambda a_{1}, \lambda a_{2}, \ldots, \lambda a_{n}$ is

The frequency distribution:
$\begin{array}{|l|l|l|l|l|l|l|} \hline X & A & 2 A & 3 A & 4 A & 5 A & 6 A \\ \hline f & 2 & 1 & 1 & 1 & 1 & 1 \\ \hline \end{array}$
where $A$ is a positive integer,has a variance of $160$. Determine the value of $A$.