Marks	Freq	Class Boundaries	Cum. Freq
23 - 25	3	22.5 - 25.5	3
26 - 28	7	25.5 - 28.5	10
29 - 31	15	28.5 - 31.5	25
32 - 34	21	31.5 - 34.5	46
35 - 37	10	34.5 - 37.5	56
38 - 40	4	37.5 - 40.5	60

(a)
(b)(i) 80th percentile = \(\frac{80 \times 60th}{100} = \text{48th mark}\).
= 31.5.
(ii) Median = \(\frac{60th}{2} = \text{30th mark} = 32.3\)
(iii) Upper quartile = \(\frac{3 \times 60th}{4} = \text{45th mark} = 35.1\)
Lower quartile = \(\frac{60th}{4} = \text{15th mark} = 29.7\)
Semi-interquartile range = \(\frac{35.1 - 29.7}{2} = 2.7\)