(i) Histogram
(ii) Ogive or Cumulative Frequency CurveHistogram
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The class limits are marked on the horizontal axis.
The frequency is marked on the vertical axis.Thus a rectangle is constructed on each class interval.
If the intervals are equal, then the height of each rectangle is proportional to the corresponding class frequency.If the intervals are unequal, then the area of each rectangle is proportional to the corresponding class frequency.
In the above example, the intervals are exclusive.
Now, let us consider an example with inclusive intervals.![]()

In table (a), the class intervals are inclusive. So, we convert them to the exclusive form as shown in table (b)
Table (b)
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(ii) A kink or a zig-zag curve is shown near the origin. It indicates that the scale along the horizontal axis does not start at the origin.
(iii) The horizontal scale and the vertical scale need not be same.![]()


When the intervals are unequal, we construct each rectangle with the class interval as the base and frequency density as the height.
Frequency density
In the above example, take second class interval,
its frequency density
Similarly for the last interval,
the frequency density
