UPSC Prelims 2015 · CSAT
Question 37: Basic Numeracy
In a group of persons travelling in a bus, 6 persons can speak Tamil, 15 can speak Hindi and 6 can speak Gujarati. In that group none can speak any other language. If 2 persons in the group can speak two languages only and one person can speak all the three languages, then how many persons are there in the group ?
AnswerUPSC’s answer is (c).
Adding 6 + 15 + 6 = 27 counts each person once for every language spoken. The 2 people with exactly two languages are counted twice, so each is counted once too often: 2 extra. The 1 person with all three is counted three times, 2 extra. Persons in the group = 27 − 2 − 2 = 23.
How you could have got this
No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong: 21 would need 6 extra counts, but only 4 are extra.
- (b) Wrong: 22 would need 5 extra counts.
- (c) Right: 27 − 2 − 2 = 23.
- (d) Wrong: 24 would need only 3 extra counts.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2015, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.