Calculation of Arithmetic Mean – Discrete Series

Mean = (å fX)/N
Where:
f = frequency
X = the variable in question
N = total no. of observations (i.e., å f)

  • Multiply the frequency of each row with the variable and obtain the total å fX.
  • Divide the total obtained in step 1 by the no. of observations (i.e., the total frequency).

Q. 3. From the following the data of the marks obtained by the 60 students of a class, obtain the average marks.

Marks No of Students Marks No. of Students
20 8 50 10
30 12 60 6
40 20 70 4

Solution. Let the marks be denoted by X and the no. of the students by f.

Marks
X
No of students
f
fX
20 8 160
30 12 360
40 20 800
50 10 500
60 6 360
70 4 280
Total N = 60 å fX = 2,460

Mean = å fX/N = 2460/60 = 41.
Hence, the average marks = 41.



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