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Question
Find the median of the following distribution:
| x | 5 | 3 | 8 | 7 | 9 | 11 |
| fi | 38 | 31 | 27 | 36 | 25 | 35 |
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Solution
Step 1: Arrange data and Calculate cumulative frequency.
First, we arrange the values of x in ascending order and calculate the cumulative frequency (cf) for each.
| x (Value) | fi (Frequency) | cf (Cumulative Frequency) |
| 3 | 31 | 31 |
| 5 | 38 | 69 (31 + 38) |
| 7 | 36 | 105 (69 + 36) |
| 8 | 27 | 132 (105 + 27) |
| 9 | 25 | 157 (132 + 25) |
| 11 | 35 | 192 (157 + 35) |
Step 2: Find the total number of observations.
The total number of observations (N) is the sum of all frequencies:
N = Σfi = 192
Since N (192) is an even number, the median is the average of the `(N/2)^(th)` and `(N/2 + 1)^(th)` observations.
`N/2 = 192/2` = 96th observation
`N/2 + 1` = 97th observation
Step 4: Identify the median value.
Now, look at the cumulative frequency (cf) column to find where the 96th and 97th observations fall:
The cf just greater than 96 and 97 is 105.
The value of corresponding to the cumulative frequency of 105 is 7.
Since both the 96th and 97th terms are 7, the average is simply 7.
The median of the distribution is 7.
