No. of days | 0-6 | 6-10 | 10-14 | 14-20 | 20-28 | 28-38 | 38-40 |
No. of students | 11 | 10 | 7 | 4 | 4 | 3 | 1 |
Solution:
Class mark, xi = (upper class limit + lower class limit)/2
No. of days | Frequency fi | Class mark xi | fixi |
0-6 | 11 | 3 | 33 |
6-10 | 10 | 8 | 80 |
10-14 | 7 | 12 | 84 |
14-20 | 4 | 17 | 68 |
20-28 | 4 | 24 | 96 |
28-38 | 3 | 33 | 99 |
38-40 | 1 | 39 | 39 |
Total | Ʃfi = 40 | Ʃfixi = 499 |
Mean = Ʃfixi/ Ʃfi
= 499/40
=12.475
Hence the mean number of days a student was absent is 12.475.