Question
Calculate the mean deviation about the mean for the following frequency distribution:
Class interval
0-4
4-8
8-12
12-16
16-20
Frequency
4
6
8
5
2

Answer

Class interval
fi
Xi
fixi
$\text{d}_\text{i}=|\text{x}_\text{i}-\bar{\text{x}}|$
fidi
0-4
4
2
8
7.2
28.8
4-8
6
6
36
3.2
19.2
8-12
8
10
80
0.8
6.4
12-16
5
14
70
4.8
24.0
16-20
2
18
36
8.8
17.6
 
N = 16
 
$\sum\text{f}_\text{i}\text{x}_\text{i}=230$
 
$\sum\text{f}_\text{i}\text{d}_\text{i}=96.0$
$\text{Mean }=\frac{\sum\text{f}_\text{i}\text{x}_\text{i}}{\text{N}}=\frac{230}{25}=9.2$
And Mean $\text{deviation}=\frac{\sum\text{f}_\text{i}\text{d}_\text{i}}{\text{N}}=\frac{96}{25}=3.84$
Hence, the required MD = 3.84

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