|
Calculation of Arithmetic Mean - Continuous
Series
Mean = å
fm/N
Where:
m = midpoint of various classes.
f = frequency of each class.
N = the total frequency
 
- Obtain the mid point of each class and denote
it by ‘m’.
Mid point = (Lower Limit
+ Upper Limit)/2
- Multiply these mid points by the respective frequency
of each class and obtain the total å
fm.
- Divide the total obtained in Step 2 by the sum
of frequencies, i.e. N.
Q.4. From the following data compute arithmetic
mean:
| Marks |
No of Students
|
Marks |
No of Students
|
| 0-10
|
5 |
30-40
|
30 |
| 10-20
|
10 |
40-50
|
20 |
| 20-30
|
25 |
50-60
|
10 |
Solution.
| Marks |
Mid points
m |
No of students
f |
f X m |
|
0-10 |
5 |
5 |
25
|
|
10-20 |
15
|
10
|
150
|
|
20-30 |
25
|
25
|
625
|
|
30-40 |
35
|
30
|
1050
|
|
40-50 |
45
|
20
|
900
|
|
50-60 |
55
|
10
|
550
|
|
Total
|
|
N
= 100 |
å
fm = 3,300 |
Mean = å fm/N = 3300/100
= 33
Hence, the average marks = 33.
|
