UPSC Prelims 2021 · CSAT
Question 9: Basic Numeracy
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 ?
AnswerUPSC’s answer is (d).
Take 100 students. Indians are 60 and foreigners 40. Girls are 50 in total. Indian girls are 30% of 60 = 18, so foreign girls are 50 − 18 = 32. Foreign boys are 40 − 32 = 8, which is 8/40 = 20% of the foreign students. Remember: assume a total of 100 in percentage problems and fill a two-way table of Indian or foreign against boys or girls.
Why each option is right or wrong
- (a) 45% would mean 18 foreign boys; only 8 of the 40 foreign students are boys.
- (b) 40% would mean 16 foreign boys; the correct count is 8.
- (c) 30% would mean 12 foreign boys; the correct count is 8.
- (d) Right: 8 boys out of 40 foreign students is 20%.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2021, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.