The table gives the distribution of marks of 60 candidates in a test.

Marks	23-25	26-28	29-31	32-34	35-37	38-40
Frequency	3	7	15	21	10	4

(a) Draw a cumulative frequency curve of the distribution.

(b) From your curve, estimate the : (i) 80th percentile ; (ii) median ; (iii) semi-interquartile range.