The following distribution shows the daily pocket allowance given to the children of a multistory building. The average pocket allowance is Rs. 18.00. Find out the missing frequency.
Class interval: | 11-13 | 13-15 | 15-17 | 17-19 | 19-21 | 21-23 | 23-25 |
Frequency: | 7 | 6 | 9 | 13 | - | 5 | 4 |
Given, Mean = 18
Let missing frequency be V
Class interval | Mid value (xi) | fi | fixi |
11-13 | 12 | 7 | 84 |
13-15 | 14 | 6 | 84 |
15-17 | 16 | 9 | 144 |
17-19 | 18 | 13 | 234 |
19-21 | 20 | V | 20V |
21-23 | 22 | 5 | 110 |
23-25 | 24 | 4 | 56 |
N = 44 + V | ∑fixi = 752 + 20V |
Mean = 
18 = 
792 + 18V = 752 + 20V
792 – 752 = 20V – 18V
40 = 2V
V = 20
19