Marks | Frequency (fi) | Deviation (di) di = (xi – 25) |
(fidi) | |
5 | 12 | -20 | -240 | |
15 | 18 | -10 | -180 | |
25 = A | 27 | 0 | 0 | |
35 | 20 | 10 | 200 | |
45 | 17 | 20 | 340 | |
55 | 6 | 30 | 180 | |
Total | ∑fi=100 | ∑(fi×di)=300 |
Let A = 25 be the assumed mean.
Then we have
Mean=A+∑fidi∑fi=25+300100=28