Question :
| Number of days | 0 – 6 | 6 – 10 | 10 – 14 | 14 – 20 | 20 – 28 | 28 – 38 | 38 – 40 |
| Number of students | 11 | 10 | 7 | 4 | 4 | 3 | 1 |
Solution :
Here, the class size varies, and \(x_i\)’s are small,
| Number of days | Mid-Value (\(x_i\)) | Number Students (\(f_i\)) | \(f_iu_i\) |
| 0 – 6 | 3 | 11 | 33 |
| 6 – 10 | 8 | 10 | 80 |
| 10 – 14 | 12 | 7 | 84 |
| 14 – 20 | 17 | 4 | 68 |
| 20 – 28 | 24 | 4 | 96 |
| 28 – 30 | 33 | 3 | 99 |
| 38 – 40 | 39 | 1 | 39 |
| Total | 40 | 499 |
Let us apply the direct method here :
So, Mean = \(\sum f_iu_i\over \sum f_i\) = \(499\over 40\) = 12.475
Hence, mean = 12.48 days
