UPSC Prelims 2021 · CSAT
Question 17: Logical Reasoning and Mental Ability
Images of consonants of the English alphabet (Capitals) are observed in a mirror. What is the number of images of these which do not look like their original shapes ?
AnswerUPSC’s answer is (b).
A mirror flips each letter left to right, so only letters symmetrical about a vertical line look unchanged. The English capitals with that symmetry are A, H, I, M, O, T, U, V, W, X and Y. Of these, A, I, O and U are vowels, leaving the consonants H, M, T, V, W, X and Y: 7. There are 21 consonants, so 21 − 7 = 14 look different in the mirror. Remember: split the alphabet into vowels and consonants first, then count only the vertically symmetric letters.
Why each option is right or wrong
- (a) 13 would mean 8 consonants look unchanged; only 7 do, so 21 − 7 = 14.
- (b) Right: 21 consonants less the 7 that are symmetrical (H, M, T, V, W, X, Y) gives 14.
- (c) 15 would mean only 6 consonants look the same; 7 do.
- (d) 16 would mean only 5 consonants look the same; 7 do.
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.