What is the mean deviation of a frequency distribution equal to?

Let the mean of $6$ observations $1, 2, 4, 5, x,$ and $y$ be $5$ and their variance be $10$. Then their mean deviation about the mean is equal to $........$.

The mean deviation from the mean for the observations $1, 3, 5, 7, 11, 13, 17, 19, 23$ is

The mean deviation about the mean of the following data is nearly:

Size $(x)$	$1$	$3$	$5$	$7$	$9$	$11$	$13$	$15$
Frequency $(f)$	$3$	$3$	$4$	$14$	$7$	$4$	$3$	$4$

Find the mean deviation about the mean for the following data.

Marks obtained	$10-20$	$20-30$	$30-40$	$40-50$	$50-60$	$60-70$	$70-80$
No of students	$2$	$3$	$8$	$14$	$8$	$3$	$2$

The mean and variance of $10$ observations are $9$ and $34.2$, respectively. If $8$ of these observations are $2, 3, 5, 10, 11, 13, 15, 21$, then the mean deviation about the median of all the $10$ observations is