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Question
A class teacher has the following absentee record of 40 students of a class for the whole term. Find the mean number of days a student was absent.
| Number of days: | 0-6 | 6-12 | 12-18 | 18-24 | 24-30 | 30-36 | 36-42 |
| Number of students: | 10 | 11 | 7 | 4 | 4 | 3 | 1 |
Solution
We will do it by a direct method
Using: mean`(∑ "f"_"i""x"_"i")/(∑ "f"_"i")`
| Number of days | Number of students (fi) |
Classmark (xi) |
fixi |
| 0-6 | 10 | `(0+6)/2 = 3` | 30 |
| 6-12 | 11 | `(6+12)/2 = 9` | 99 |
| 12-18 | 7 | `(12+18)/2 =15` | 105 |
| 18-24 | 4 | `(18+24)/2 = 21` | 84 |
| 24-30 | 4 | `(24+30)/2 =27` | 108 |
| 30-36 | 3 | `(30+46)/2 =33` | 99 |
| 36-42 | 1 | `(36+42)/2 = 39` | 39 |
| ∑ fi = 40 | ∑ fixi =564 |
substituting the values in the formula
mean = `564/40 = 14.1`
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