Statistics
 Mean of grouped data using direct method
Mean , where fi is the frequency corresponding to the class mark xi.
Example:
Consider the following distribution of marks scored by the students of a class in a unit test.
Marks scored 
10 – 20 
20 – 30 
30 – 40 
40 – 50 
Number of students 
4 
7 
15 
14 
Find the mean marks obtained by the students
Solution:
Class interval 
Frequency (f_{i}) 
Class mark(x_{i}) 
f_{i}x_{i} 
10 – 20 
4 
15 
60 
20 – 30 
7 
25 
175 
30 – 40 
15 
35 
525 
40 – 50 
14 
45 
630 
Total 



Mean
Thus, the mean of the marks obtained by the students is 34.75.
 Assumedmean method
, where ‘a’ is the assumed mean, d_{i} = x_{i} – a, and f_{i}_{ }is the frequency corres…
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