Frequency Diagrams and Frequency Polygons
When data is grouped with equal intervals, work out the midpoint.
A frequency diagram can be drawn then with the midpoint along the horizontal (x-axis) and the frequency along the vertical (y-axis)
A frequency polygon is formed by joining the midpoints of the tops of the bars in a frequency diagram.
- Example 1. Draw a frequency diagram and frequency polygon of the grouped data:
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(a) For each range of Marks work out the midpoint x
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(b) Frequency diagram
(c) Frequency polygon
to: 
