A histogram consists of a set of adjacent rectangles whose bases are marked off by class boundaries on the x-axis and whose heights proportional to the frequencies associated with respective classes. The area of each rectangle represents the respective class frequencies.
1. Histogram for equal class intervals.
Example
2. Histogram for unequal class intervals.
(a). Frequency density method
If the class intervals of the distribution are different, then the heights of the bars are proportional to the frequency density.
Frequency density = frequency / class width
In this we have to draw histogram using frequency density instead of frequency
image taken from http://passmath.co.uk/gcse-mathematics.html
(b) Height of the rectangle
If the class intervals of the distribution are different, then
height of rectangle=frequency/standard
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