Let the assumed mean (A) = 25
Marks (xi) |
Frequency (fi) |
ui = xi - A = xi - 25 |
fiui |
15 |
5 |
-10 |
-50 |
20 |
8 |
-5 |
-40 |
22 |
11 |
-3 |
-33 |
24 |
20 |
-1 |
-20 |
25 |
23 |
0 |
0 |
30 |
18 |
5 |
90 |
33 |
13 |
8 |
104 |
38 |
3 |
13 |
39 |
45 |
1 |
20 |
20 |
|
N = 102 |
|
\(\sum\)fiui = 110 |
Average number of marks = A + \(\frac{\sum f_iu_i}{N}\)
\(=25+\frac{110}{102}=\frac{2550+110}{102}\)
\(=\frac{2660}{102}=26.08\) (approx)