Consider the following arrangement that has some missing letters : abab_b_bcb_dcdcded_d The missing letters which complete the arrangement are
- (a) a, b, c, d
- (b) a, b, d, e
- (c) a, c, c, e ✓ UPSC's answer
- (d) b, c, d, e
Why the answer is (c)
• Fill the blanks with a, c, c, e: abab(a)b(c)bcb(c)dcdcded(e)d.
• The completed series reads ababab cbcb cdcdcd eded.
• It is built from alternating pairs: ab three times, cb twice, cd three times and ed twice — the letters move forward one step at each change.
• Hence option (c).
Why the other options are wrong
- (a) a, b, c, d
- Option (a) suggests the second missing letter is 'b', but the pattern requires 'c' to maintain the sequence logic.
- (b) a, b, d, e
- Option (b) suggests the third missing letter is 'd', but the pattern requires 'c' to complete the specific sub-sequence.
- (d) b, c, d, e
- Option (d) suggests the first missing letter is 'b', but the sequence starts with 'a' to continue the 'abab' pattern.
Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2020, held on 4 October 2020. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.