2013 CSAT, all questions
UPSC Prelims 2013 · CSAT
Question 34: Logical Reasoning and Mental Ability
In a class of 45 students, a boy is ranked 20th. When two boys joined, his rank was dropped by one. What is his new rank from the end ?
a25th
b26th
c27th
d28th
AnswerUPSC’s answer is (c).
Rank 20 means 19 boys ahead of him. When two boys join and his rank drops by one to 21, exactly one of the new boys has come in ahead of him and the other behind. The class now has 47 students. His rank from the end is 47 - 21 + 1 = 27. As a check, with 21st from the top there are 26 boys behind him, so he is 27th from the end.
Why each option is right or wrong
- (a) Wrong. 25th from the end would make him 23rd from the top.
- (b) Wrong. 26th was his rank from the end before the two boys joined.
- (c) Right. 47 - 21 + 1 = 27.
- (d) Wrong. 28th from the end would make him 20th from the top; his rank did change.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2013, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.