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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 = xia, and fi is the frequency corres…

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