While entering the test marks of a class, Arun's marks were entered as 98 instead of 68. As a result, the average marks of the cl…

Question

While entering the test marks of a class, Arun's marks were entered as 98 instead of 68. As a result, the average marks of the class increased by 0.5.

What is the number of pupils in the class?

1. A. 10
2. B. 20
3. C. 60 (Correct answer)
4. D. 73

Correct Answer

Option C — 60

Detailed Solution & Explanation

The correct answer is 60.

Key Points

• The recorded mark exceeded the true mark by 98 − 68 = 30.
• That single excess of 30 raised the class average by 0.5.
• Since an excess of E spread over n pupils raises the mean by E ÷ n, we need 30 ÷ n = 0.5.
• So n = 30 ÷ 0.5 = 60 pupils.

Additional Information

• The relation to remember: change in total = change in mean × number of items.
• Here the total changed by 30 while the mean changed by 0.5, which pins the class size at 60 without needing any actual marks.

*Ministry of Papers worked solution. The Commission has not yet published the official key for this paper; this answer will be reconciled with it on release.*