UPSC PREVIOUS-YEAR QUESTIONS

Series Completion

Practise the original questions with answers and explanations.

2 questions

Question 12024 · CSAT

24. 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

Answer: C

Explanation

Let’s analyze the given sequence: A_BCD_BBCDABC_DABC_D. The pattern appears to be a repeating block where one letter is duplicated in each subsequent block. Let’s assume the base block is ABCD. The pattern seems to be:
1. A A BCD (A is duplicated)
2. A B BCD (B is duplicated)
3. A B C C D (C is duplicated)
4. A B C D D (D is duplicated)
Applying this pattern to the given sequence:
– For A_BCD, the first block should be A A BCD. So, the first blank is A.
– For _BBCD, the second block should be A B BCD. So, the second blank is A.
– For ABC_D, the third block should be A B C C D. So, the third blank is C.
– For ABC_D, the fourth block should be A B C D D. So, the fourth blank is D.
Therefore, the missing letters are A, A, C, D. This is a complex series completion problem requiring careful pattern recognition.

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Question 22023 · CSAT

Consider the sequence ABC_ _ABC_DABBCD_ABCD that follows a certain pattern. Which of the following completes the sequence?

A. DACB
B. CDAB
C. DCCA
D. DDCA

Answer: D

Explanation

The given sequence is ABC_ _ABC_DABBCD_ABCD. Let’s analyze the pattern by dividing the sequence into blocks of 4 or 5 characters. The provided solution suggests a cyclic shift pattern when divided into blocks of 4, where the last character of a block moves to the first position of the next block. If we assume the complete sequence follows the pattern: ABCD, DABC, CDAB, BCDA, ABCD. Let’s map this to the given sequence with blanks:
1. ABC_ -> ABCD (Blank is D)
2. _ABC -> DABC (Blank is D)
3. _DAB -> CDAB (Blank is C)
4. BCD_ -> BCDA (Blank is A)
5. ABCD -> ABCD (No blank)
So, the missing letters are D, D, C, A. This matches option (D). The pattern is a cyclic shift of the letters A, B, C, D. This question tests pattern recognition in sequences, a common logical reasoning topic in CSAT.

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