Difficulty: Medium
Correct Answer: babba
Explanation:
Introduction / Context:
This is a letter-series completion question where several characters are missing and shown as blanks (underscores). Your job is to identify the repeating pattern in the visible letters, then fill every blank in order to keep the series consistent. Finally, you must pick the option that matches the exact sequence of missing letters placed into the blanks from left to right.
Given Data / Assumptions:
The series is shown with underscores representing missing letters, and the missing letters must be filled in the same order as the blanks appear. After filling, the entire string should follow one repeating logical pattern.
Concept / Approach:
A reliable method for such questions is to look for a repeating chunk pattern (a block that repeats again and again). Here, the visible parts strongly suggest alternating blocks made of a and b. If we can rewrite the series into equal-sized blocks (such as 3-letter blocks), we can test whether a particular repeating block (like baa and bba) keeps appearing. Once the repeating block is identified, each underscore can be determined by checking what letter is required at that position to preserve the repeating structure. This avoids guessing and makes the answer deterministic.
Step-by-Step Solution:
Step 1: Write the series with blanks: _ a _ b _ abaa _ bab _ abbStep 2: Try to see if the text can be viewed as repeating 3-letter blocks (common in a/b series).Step 3: Notice the long visible segments contain a lot of "baa" and "bba" shapes: for example, "abaa" contains "baa" and "bab" is a near-rotation of these blocks.Step 4: Test a simple repeating pair of 3-letter blocks: baa / bba repeating.Step 5: If the pattern is baa, bba, baa, bba, ... then the overall series should look like: baa / bba / baa / bba / baa / bb (last block may be incomplete).Step 6: Now match this target form to the given string: _ a _ must become "baa" so the missing letters there are b (before a) and a (after a).Step 7: Next, "b _" should complete "bba", so the missing letter after b is b.Step 8: The segment "abaa _" should align with "... baa / bba ...". The ending underscore after "abaa" must be a to complete the expected continuation.Step 9: The segment "bab _" must continue the same baa/bba repetition; the missing letter here must be b to maintain the required next block.Step 10: Collect the missing letters in order of blanks: b, a, b, b, a which forms "babba".
Verification / Quick Check:
Substitute the missing letters "babba" back into the series: b a a b b abaa a bab b abb. When regrouped into 3-letter chunks, it aligns as baa / bba / baa / bba / baa / bb, which confirms the repeating baa/bba pattern and shows the blanks were filled consistently. Because the pattern check works across the entire sequence (not just one local spot), the result is stable and not coincidental.
Why Other Options Are Wrong:
aaabb: Starts the first block with a, which breaks the expected "baa" beginning needed around "_ a _".
ababb: Forces the second blank to be b, but the first 3-letter block would become "bbb" or "bab" in the wrong place, breaking repetition.
babab: Alternates too aggressively and prevents forming the stable 3-letter blocks baa and bba through the full string.
bbaba: Makes the early portion "_ a _" become "baa" incorrectly or disrupts the later completion near "bab _".
Common Pitfalls:
Many learners try to guess the option by looking only at the first one or two blanks, but that often produces multiple seemingly plausible starts. Another pitfall is ignoring block grouping and treating the series as random alternation of a and b. In these problems, grouping into fixed-size chunks (like 3 letters here) is usually the intended key. Also, be careful to collect missing letters strictly in left-to-right blank order; mixing the order will lead to a wrong option even if you found correct letters at individual positions.
Final Answer:
The missing letters are babba.
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