The marks obtained out of 50, by 102 students in a Physics test are given in the frequency table below:
Marks (x): | 15 | 20 | 22 | 24 | 25 | 30 | 33 | 38 | 45 |
Frequency (f): | 5 | 8 | 11 | 20 | 23 | 18 | 13 | 3 | 1 |
Find the average number of marks.
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 | ∑fiui = 110 |
Average number of marks = A + 
= 25 + 
= 
= 
= 26.08 (approx)
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