CSAT 2024

Q. Consider the sequence A_BCD_BBCDABC_DABC_D that follows a certain pattern.

Which one of the following completes the sequence?
a) B, A, D, C
b) B, A, C, D
c) A, A, C, D
d) A, A, D, C
Correct answer: c) A, A, C, D

Question from UPSC Prelims 2024 CSAT

Explanation : 

Solution Steps

  1. Let’s split the sequence in sets of 5 character: A_BCD_BBCDABC_DABC_D Splits into: A_BCD / _BBCD / ABC_D / ABC_D
  2. Analyzing this grouping, we can identify the pattern:
    • Each group consists of 5 characters
    • The pattern involves repeating ABCD in various arrangements, sometimes with repetitions
  3. The correct grouping of the sequence by Hit & Trail Method is: A A BCD A BBCD ABC C D ABC D D (Hit & Trail)
  4. Observations from this pattern:
    • The first group has two A’s followed by BCD
    • The second group starts with A, then has two B’s, followed by CD
    • The third group has ABC, then C, then D
    • The fourth group has ABC, then two D’s
  5. The last group in our given sequence is incomplete: ABC_D
  6. To complete it according to the established pattern, we need to add another D, making it: ABC D D
  7. Therefore, the missing letters are A, A, C, D
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