UPSC Prelims 2015 · CSAT
Question 9: Basic Numeracy
Twelve people form a club. By picking lots, one of them will host a dinner for all once in a month. The number of dinners a particular member has to host in one year is
AnswerUPSC’s answer is (d).
Each month the host is chosen by drawing lots among the twelve, and each draw is independent of the earlier ones. So a given member might be picked in several months, or never. Over twelve months the average is one dinner per member, but no individual count is fixed: it can be anything from zero to twelve. Only a fixed rotation would guarantee one dinner each. Since lots are drawn, the number cannot be predicted.
Why each option is right or wrong
- (a) Wrong: one dinner each is only the average over twelve people, not guaranteed for any one member.
- (b) Wrong: zero is possible but not certain; the member may well be drawn.
- (c) Wrong: three is possible but no more certain than any other number.
- (d) Right: independent monthly draws can give a member anywhere from zero to twelve dinners.
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.