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Question
Construct a frequency polygon without using a histogram for the following frequency distribution :
| Class Interval | 10-20 | 20-40 | 40-60 | 60-80 | 80-100 |
| Frequency | 9 | 17 | 15 | 20 | 14 |
Solution
Steps :
1. Find class mark by calculating the average of the class interval.
2. On the x-axis , take 1 cm as 5 units and plot class interval.
3. On the y-axis , take 1 cm as 5 units and plot frequency.
4. plot the points on the graph. (15,9),(30,17),(50,15),(70,20),(90,14).
5. Mark two more midpoints of zero frequency on x-axis at the start and at the end .
6. Now connect the points using staright lines.
| Class Interval | Class mark | Frequency |
| 10-20 | `= (10+20)/2 = 15` | 9 |
| 20-40 | `= (20+40)/2 = 30` | 17 |
| 40-60 | `= (40+60)/2 = 50` | 15 |
| 60-80 | `= (60 + 80)/2 = 70` | 20 |
| 80-100 | `= (80 + 100)/2 = 90` | 14 |
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Try yourself
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