UPSC Prelims 2021 · CSAT
Question 56: Logical Reasoning and Mental Ability
In a code language ‘MATHEMATICS’ is written as ‘LBSIDNZUHDR’. How is ‘CHEMISTRY’ written in that code language ?
AnswerUPSC’s answer is (b).
Compare each letter of MATHEMATICS with its code LBSIDNZUHDR: M to L is one step back, A to B one step forward, T to S back, H to I forward, and so on, alternating back and forward by one. Apply this to CHEMISTRY: C−1 = B, H+1 = I, E−1 = D, M+1 = N, I−1 = H, S+1 = T, T−1 = S, R+1 = S, Y−1 = X. The code is BIDNHTSSX. Remember: list the shift for every position in the example; patterns often alternate.
Why each option is right or wrong
- (a) DIDLHRSSX gets the 1st, 4th and 6th letters wrong; those shifts should be −1, +1 and +1.
- (b) Right: BIDNHTSSX alternates −1, +1 from the first letter.
- (c) BIDLHTSSX has L for M; the fourth shift should be +1, giving N.
- (d) DGFLIRUQZ starts with the wrong shift (+1 for C) and leaves the fifth letter unshifted.
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.