How histograms can be conveniently converted into small frequencies when class intervals are equal?
When class intervals are equal i.e. when all rectangles have the same base, area can conveniently be represented by the frequency of any interval for purposes of comparison. When bases vary in their width, the heights of rectangles are to be adjusted to yield comparable measurements. In such a situation frequency density (class frequency divided by width of the class interval) instead of absolute frequency.