Reasoning : Logical Reasoning & Analytical Ability

Q 101 / 325

UPSC CSE Prelims 2021

In the series_b_a_ba_b_abab_aab; fill in the six blanks (_) using one of the following given four choices such that the series follows a specific order.

EXPLANATION

Correct Option (4)

The given series is `_ b _ a _ ba _ b _ abab _ aab`. To identify the correct sequence for the blanks, we must determine the underlying pattern of the series.

Upon analyzing the structure, the series follows a repeating block pattern of `(abb)(aab)`. This block is repeated three times consecutively:

  • First block: `a b b`
  • Second block: `a a b`
  • Third block: `a b b`
  • Fourth block: `a a b`
  • Fifth block: `a b b`
  • Sixth block: `a a b`

When this pattern `a b b a a b a b b a a b a b b a a b` is applied to the original series with blanks, the characters filling the blanks are:

  • Blank 1: `a`
  • Blank 2: `b`
  • Blank 3: `a`
  • Blank 4: `b`
  • Blank 5: `a`
  • Blank 6: `b`

Thus, the sequence `ababab` correctly completes the series, forming a consistent repeating pattern.

Incorrect Options:

Substituting the sequences from the other options into the blanks does not yield a consistent or discernible repeating pattern:

  • Option 1 (bababa): Inserting `bababa` results in `b b a a b b a b b a a b a b a a b`. This sequence does not exhibit a uniform repeating block.
  • Option 2 (baabba): Inserting `baabba` results in `b b b a a a a b b b a a b b a a b`. This sequence lacks a clear, consistent pattern.
  • Option 3 (bbaabb): Inserting `bbaabb` results in `b b b a a a a b b b a a b b b a a b`. This arrangement also fails to establish a regular repeating pattern.