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Question
The class marks of a frequency distribution are: 27, 32, 37, 42, 47, 52, 57, 62, 67, 72 and 77. Find the class size and true class limits.
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Solution
The class marks are uniformly spread.
∴ The class size is the difference between any two consecutive class marks.
Class size
= 32 - 27
= 5
The lower limit of the first class
= `27 - (5)/(2)`
= 27 - 2.5
= 24.5
The upper limit of the first class
= `27 + (5)/(2)`
= 27 + 2.5
= 29.5
Thus, the first class interval is 24.5 - 29.5
Similarly, we can find the class limits of all the class marks given.
| Class Marks | Class limits |
| 27 | 24.5 - 29.5 |
| 32 | 29.5 - 34.5 |
| 37 | 34.5 - 39.5 |
| 42 | 39.5 -- 44.5 |
| 47 | 44.5 - 49.5 |
| 52 | 49.5 - 54.5 |
| 57 | 54.5 - 59.5 |
| 62 | 59.5 - 64.5 |
| 67 | 64.5 - 69.5 |
| 72 | 69.5 - 74.5 |
| 77 | 74.5 - 79.5 |
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