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GATE DA 2025 Q15: Propositional logic: which statements are equivalent?

Question

Let pp and qq be any two propositions. Consider the following propositional statements.

S1:p→q,S2:¬p∧q,S3:¬p∨q,S4:¬p∨¬q,S_1 : p \rightarrow q, \quad S_2 : \neg p \wedge q, \quad S_3 : \neg p \vee q, \quad S_4 : \neg p \vee \neg q,

where ∧\wedge denotes conjunction (AND operation), ∨\vee denotes disjunction (OR operation), and ¬\neg denotes negation (NOT operation). Which one of the following options is correct? (Note: ≡\equiv denotes logical equivalence)

Try it: multiple choice: exactly one correct option

Select one option
Wrong answer costs 1/3 mark in GATE.
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Answer: A (official GATE 2025 final answer key)

Concept used: Implication equivalence: p→q≡¬p∨qp \rightarrow q \equiv \neg p \vee q.

First step: Rewrite the implication S1S_1 using only ¬\neg and ∨\vee, then compare it with the other three statements.

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Source: official GATE 2025 DA question paper and final answer key, organised by IIT Roorkee. Question paper · Answer key