Marks	Freq	Class boundary	Class width	Height
10 - 14	14	9.5 - 14.5	5	2.8
15 - 24	30	14.5 - 24.5	10	3
25 - 29	22	24.5 - 29.5	5	4.4
30 - 39	18	29.5 - 39.5	10	1.8
40 - 44	12	39.5 - 44.5	5	2.4
45 - 49	4	44.5 - 49.5	5	0.8

Since the class intervals are not equal, we draw the histogram in a way that the area of the bars, rather than the height must be proportional to the frequency. On the vertical scale, we plot frequency density instead of frequency where frequency density = frequency/ class width.