In a class, 60% of students are from India and 50% of the students are girls. If 30% of the Indian students are girls, then what percentage of foreign students are boys ?

(a) 45%
(b) 40%
(c) 30%
(d) 20% ✓ UPSC's answer

Why the answer is (d)

• Assume the total number of students is 100 for easy calculation.

• 60% are Indian students, so there are 60 Indian students and 40 foreign students.

• 30% of the Indian students are girls, which means 0.30 * 60 = 18 Indian girls.

• 50% of the total students are girls, so there are 50 girls in total.

• The number of foreign girls is the total girls minus Indian girls: 50 - 18 = 32 foreign girls.

• The number of foreign boys is the total foreign students minus foreign girls: 40 - 32 = 8 foreign boys.

• The percentage of foreign students who are boys is (8 / 40) * 100 = 20%.

Why the other options are wrong

(a) 45%: 45% is incorrect because the calculation of foreign boys (8) divided by total foreign students (40) yields 20%, not 45%.
(b) 40%: 40% is incorrect because it likely confuses the total percentage of foreign students with the specific percentage of boys among them.
(c) 30%: 30% is incorrect because it mistakenly uses the percentage of Indian girls (30%) as the answer for foreign boys.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2021, held on 10 October 2021. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.