Calculate the mean deviation from the median of the following data:

Class interval	$0-6$	$6-12$	$12-18$	$18-24$	$24-30$
Frequency	$4$	$5$	$3$	$6$	$2$

(7) Step $1$: Find the cumulative frequency $(cf)$ and total frequency $(N)$.

Class interval	$f_i$	$x_i$	$cf$
$0-6$	$4$	$3$	$4$
$6-12$	$5$	$9$	$9$
$12-18$	$3$	$15$	$12$
$18-24$	$6$	$21$	$18$
$24-30$	$2$	$27$	$20$

Step $2$: Find the median class.
Since $N = 20$,$\frac{N}{2} = 10$. The cumulative frequency just greater than $10$ is $12$,so the median class is $12-18$.
Step $3$: Calculate the median $(M_d)$.
$M_d = l + \left( \frac{\frac{N}{2} - C}{f} \right) \times h = 12 + \left( \frac{10 - 9}{3} \right) \times 6 = 12 + 2 = 14$.
Step $4$: Calculate mean deviation $(MD)$.
$MD = \frac{\sum f_i |x_i - M_d|}{N} = \frac{4|3-14| + 5|9-14| + 3|15-14| + 6|21-14| + 2|27-14|}{20} = \frac{4(11) + 5(5) + 3(1) + 6(7) + 2(13)}{20} = \frac{44 + 25 + 3 + 42 + 26}{20} = \frac{140}{20} = 7$.