The following table shows the classification of percentages of marks of students and the number of students. Draw a frequency polygon from the table.
| Result (Percentage) | 30–40 | 40–50 | 50–60 | 60–70 | 70–80 | 80–90 | 90–100 |
|---|---|---|---|---|---|---|---|
| No. of students | 7 | 33 | 45 | 65 | 47 | 18 | 5 |
Answer: Plot (35, 7), (45, 33), (55, 45), (65, 65), (75, 47), (85, 18), (95, 5) and join them, closing at (25, 0) and (105, 0)
| Class | Class mark | Frequency | Point |
|---|---|---|---|
| 30–40 | 35 | 7 | (35, 7) |
| 40–50 | 45 | 33 | (45, 33) |
| 50–60 | 55 | 45 | (55, 45) |
| 60–70 | 65 | 65 | (65, 65) |
| 70–80 | 75 | 47 | (75, 47) |
| 80–90 | 85 | 18 | (85, 18) |
| 90–100 | 95 | 5 | (95, 5) |
Take class marks (percentage of marks) on the X-axis and number of students on the Y-axis with a convenient scale. Plot the points and also the points (25, 0) and (105, 0), which are the class marks of the imaginary classes just before the first and just after the last class (frequency 0). Join all the points in order by line segments:
(25, 0), (35, 7), (45, 33), (55, 45), (65, 65), (75, 47), (85, 18), (95, 5), (105, 0)
The closed figure obtained with the X-axis is the required frequency polygon.
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