Engineering Mathematics · Combinatorics
Official IIT answer key · IIT Guwahati · Audited Aug 2026
GATE CSE 2025 Set 1 Q30 · NAT · 1 mark
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Topic notes
GATE evaluates Generating Functions by testing the candidate's ability to find closed-form representations of ordinary generating functions (OGFs) for piecewise or parity-dependent sequences. Questions require decomposing sequences linearly and applying operations like substitution (e.g., x2) and differentiation to handle polynomial coefficients. These items test analytical fluency with infinite series and discrete mathematics manipulations.
Full Combinatorics guide →Let S be the set of all ternary strings defined over the alphabet \a, b, c\. Consider all strings in S that contain at least one occurrence of two consecutive symbols, that is, “aa”, “bb” or “cc”. The number of such strings of length 5 that are possible is … (Answer in integer)
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Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.
