Calculate 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

Solution: First we have to construct a table for the given data. Please refer to video for creating complete table.
Here, $N=\sum f_i=20$
$\therefore \frac{N}{2}=\frac{20}{2}=10$
So, median class will be $6-12$.
Now,
Median, $M=l+\left(\frac{\frac{N}{2}-c.f.}{f}\right)\ast h$
Here, $l$ = lower limit of median class = $12$
$N$ = Total frequency = $20$
$c.f.$ = Cumulative frequency of pre median class$=9$
$f$ = Frequency of median class = $3$
$h$ = Class size $=6$
$\therefore Median=12+\left(\frac{10-9}{3}\right)\ast 6=12+2=14$
Now, we will find the deviation from the median of the mid value of each class.
$\therefore \left|d_i\right|=11,5,1,7,13$
$\therefore f_i{d}_i=44,25,3,42,26$
$\therefore \sum f_i{d}_i=140$
$\therefore$ Mean deviation $=\frac{\sum f_i{d}_i}{N}=\frac{140}{20}=7.$