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 (fi) |
Class mark(xi) |
fixi |
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.
- Assumed-mean method
, where ‘a’ is the assumed mean, di = xi – a, and fi is the frequency corres…
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