UPSC Prelims 2024·CSAT·Logical Reasoning·Series and Sequences

Consider the sequence: ABC _ _ ABC _ DABBCD _ ABCD Which one of the following completes the sequence?

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Last updated 23 May 2026, 3:31 pm IST
  1. ADACB
  2. BCDABCorrect
  3. CDCCA
  4. DDDCA

Explanation

There are 4 blanks in the sequence: ABC _ _ ABC _ DABBCD _ ABCD Filling the four blanks with option B (C, D, A, B in order) gives: A B C C D A B C A D A B B C D B A B C D Splitting this 20-letter string into four blocks of five letters reveals the pattern: • Block 1: A B C C D — letter C is the repeated extra • Block 2: A B C A D — letter A is the repeated extra • Block 3: A B B C D — letter B is the repeated extra • Block 4: B A B C D — closing block in the cycle Each block contains the letters A, B, C, D with one extra letter inserted at a cyclic position. Only the substitution C, D, A, B (option B) produces this coherent 5-letter pattern while matching the fixed segments (ABC, DABBCD, ABCD) already given. Therefore, the answer is B (CDAB).
Logical Reasoning: Consider the sequence: ABC _ _ ABC _ DABBCD _ ABCD Which one of the following completes the sequence?
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