Mathematics
Calculate the mean of the following distribution using step deviation method :
| Marks | Number of students |
|---|---|
| 0 - 10 | 10 |
| 10 - 20 | 9 |
| 20 - 30 | 25 |
| 30 - 40 | 30 |
| 40 - 50 | 16 |
| 50 - 60 | 10 |
Measures of Central Tendency
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Answer
We construct the following table, taking assumed mean a = 25.
Here, c (width of each class) = 10.
| Marks (Classes) | Class mark (yi) | No. of students (Frequency (fi)) | fiui | |
|---|---|---|---|---|
| 0 - 10 | 5 | -2 | 10 | -20 |
| 10 - 20 | 15 | -1 | 9 | -9 |
| 20 - 30 | 25 | 0 | 25 | 0 |
| 30 - 40 | 35 | 1 | 30 | 30 |
| 40 - 50 | 45 | 2 | 16 | 32 |
| 50 - 60 | 55 | 3 | 10 | 30 |
| Total | 100 | 63 |
Hence, mean of the following distribution is 31.3
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