# 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

- Let’s split the sequence in sets of 5 character: A_BCD_BBCDABC_DABC_D Splits into: A_BCD / _BBCD / ABC_D / ABC_D
- 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

- The correct grouping of the sequence by Hit & Trail Method is: A A BCD A BBCD ABC C D ABC D D (Hit & Trail)
- 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

- The last group in our given sequence is incomplete: ABC_D
- To complete it according to the established pattern, we need to add another D, making it: ABC D D
- Therefore, the missing letters are A, A, C, D