Concept:The average marks are calculated from a cumulative frequency distribution by first converting it into a regular frequency table, then using the weighted mean formula: average = sum(midpoint × frequency) / total candidates.
Explanation:From the "more than" data, the class intervals are: 10–20, 20–30, 30–40, and 40 and above.
Subtract successive cumulative frequencies to get each class frequency:
10–20: 100 – 75 = 25
20–30: 75 – 60 = 15
30–40: 60 – 40 = 20
40 and above: 40 (since all 40 candidates have marks above 40)
Midpoints: (10+20)/2 = 15, (20+30)/2 = 25, (30+40)/2 = 35, and for the open‑ended class assume midpoint = 45.
Now find sum of (midpoint × frequency):
15×25=37525×15=37535×20=70045×40=1800Total =
375+375+700+1800=3250Total number of candidates = 100.
Average marks =
3250/100=32.5Answer:Average marks = 32.5 (Option D)