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Question
Construct a frequency polygon without using a histogram for the following frequency distribution :
| Class Interval | 1-10 | 11-20 | 21-30 | 31-40 | 41-50 |
| Frequency | 8 | 12 | 10 | 16 | 6 |
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Solution
Steps :
1. Make the class intervals continuous by subtracting 0.5 from the lower limit of each class and add 0.5 to the upper limit of each class .
2. Find class mark by calculating the average of the class interval.
3. On the x-axis , take 1 cm as 5 units and plot class interval.
4. On the y-axis , take 1 cm as 5 units and plot frequency.
5. Plot the points on the graph. (5.5,8),(15.5,12),(25.5,10),(35.5,16),(45.5,6).
6. Mark two more midpoints of zero frequency on x-axis at the start and at the end.
7. Now connect the points using straight lines.
| Class Interval | Class Mark | Frequency |
| 0.5-10.5 | = `(0.5+10.5)/2 = 5.5` | 8 |
| 10.5-20.5 | = `(10.5+20.5)/2 = 15.5` | 12 |
| 20.5-30.5 | = `(20.5 + 30.5)/2 = 25.5` | 10 |
| 30.5-40.5 | = `(30.5 + 40.5)/2 = 35.5` | 16 |
| 40.5-50.5 | = `(40.5 + 50.5)/2 = 45.5` | 6 |
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