Consider the sequence ABC_ _ ABC_ DABBCD_ ABCD that follows a certain pattern. Which one of the following completes the sequence ?
- (a) DACB
- (b) CDAB
- (c) DCCA
- (d) DDCA ✓ UPSC's answer
Why the answer is (d)
• The sequence is composed of four 4-letter blocks: 'ABC_', '_ABC', '_DAB', 'BCD_'.
• Analyzing the first block 'ABC_', the missing letter must be 'D' to form the set {A, B, C, D}, making it 'ABCD'.
• Analyzing the second block '_ABC', the missing letter must be 'D' to form the set {A, B, C, D}, making it 'DABC'.
• Analyzing the third block '_DAB', the missing letter must be 'C' to form the set {A, B, C, D}, making it 'CDAB'.
• Analyzing the fourth block 'BCD_', the missing letter must be 'A' to form the set {A, B, C, D}, making it 'BCDA'.
• Combining the missing letters in order gives 'D', 'D', 'C', 'A', which corresponds to option (d).
Why the other options are wrong
- (a) DACB
- Option (a) DACB implies the second block is 'CABC' and the third is 'D DAB', which do not contain the complete set {A, B, C, D}.
- (b) CDAB
- Option (b) CDAB implies the first block is 'ACBC' and the second is 'DABC', where the first block lacks 'D' and has a duplicate 'C'.
- (c) DCCA
- Option (c) DCCA implies the second block is 'CABC' and the third is 'D DAB', which do not contain the complete set {A, B, C, D}.
Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2023, held on 28 May 2023. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.