The mean of the following distribution is 18. Find the frequency f of the class 19 - 21
The mean of the following distribution is 18. Find the frequency f of the class 19 - 21.
| Class | 11-13 | 13-15 | 15-17 | 17-19 | 19-21 | 21-23 | 23-25 |
| Frequency | 3 | 6 | 9 | 13 | f | 5 | 4 |
Answer
| Class | Frequency, f | Mid Value, x | fixi |
| 11-13 | 3 | 12 | 36 |
| 13-15 | 6 | 14 | 84 |
| 15-17 | 9 | 16 | 144 |
| 17-19 | 13 | 18 | 234 |
| 19-21 | f | 20 | 20f |
| 21-23 | 5 | 22 | 110 |
| 23-25 | 4 | 24 | 96 |
| Σfi = 40 + f | Σfixi = 704 + 20f |
Mean = 18 = (704 + 20f)/(40 + f)
720 + 18f = 704 + 20f
f = 8