Let $S$ be the set of all values of $a_1$ for which the mean deviation about the mean of $100$ consecutive positive integers $a_1, a_2, a_3, \ldots, a_{100}$ is $25$. Then $S$ is

The following data represents the frequency distribution of $20$ observations.

$x_i$	$3$	$4$	$5$	$8$	$10$	$11$
$f_i$	$\alpha+2$	$(\alpha-1)^2$	$4$	$\alpha-1$	$2$	$\alpha$

Then its mean deviation about the mean is

Calculate the mean deviation about the mean of the set of first $n$ natural numbers when $n$ is an odd number.

Find the mean deviation about the median of the following distribution:
$ \begin{array}{|l|l|l|l|l|l|} \hline \text{Marks obtained} & 10 & 11 & 12 & 14 & 15 \\ \hline \text{Number of students} & 2 & 3 & 8 & 3 & 4 \\ \hline \end{array} $

The mean deviation about the median for the following data $6, 3, 4, 9, 2, 7, 11$ is

If $M_1$ and $M_2$ are the mean deviations from the mean and median of the first $15$ even integers,then $M_1+M_2=$