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Propositional and First-Order Logic

GATE CSE 2011 · Q30

MCQ2 marksMedium

Time

Which one of the following options is CORRECT given three positive integers xx, yy and zz, and a predicate P(x)=eg(x=1)∧∀y((∃z(x=y∗z))⇒(y=x)∨(y=1))P(x) = eg (x = 1) \land \forall y ((\exists z (x = y * z)) \Rightarrow (y = x) \lor (y = 1))

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Solution

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Official answer: A) P(x) being true means that x is a prime number

Propositional and First-Order Logic

Let us analyze the components of the given predicate P(x)P(x) in the domain of positive integers:

  1. $

eg(x = 1)assertsthat asserts that x \neq 1$.

  1. ∃z(x=y⋅z)\exists z (x = y \cdot z) means that yy is a factor (divisor) of xx, since there exists a positive integer zz such that y⋅z=xy \cdot z = x.

  2. The implication (∃z(x=y⋅z))  ⟹  (y=x∨y=1)(\exists z (x = y \cdot z)) \implies (y = x \lor y = 1) asserts that for every positive integer yy, if yy divides xx, then yy must be either xx or 11.

Combining these two parts:

  • xx is a positive integer not equal to 11.

  • The only positive divisors of xx are 11 and xx itself.

This is precisely the definition of a prime number.

Therefore, P(x)P(x) being true means that xx is a prime number, which corresponds to option (A) [p1].

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This Propositional and First-Order Logic previous year question is Q30 of the GATE CSE 2011 paper. Find more GATE CSE PYQs on Propositional and First-Order Logic in Engineering Mathematics, or browse all GATE CSE PYQs.

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Propositional and First-Order Logic in GATE CSE

Propositional and First-Order Logic has 18 GATE CSE PYQs across 16 papers from 2011 to 2026. 7 of them are 2-mark MCQs like this one, and it is the only one in GATE CSE 2011.

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GateAI solution cardGATE CSE 2011 · Q30 · MCQ

Which one of the following options is CORRECT given three positive integers x, y and z, and a predicate P(x) = eg (x = 1) ∧ ∀ y ((∃ z (x = y * z)) ⇒ (y = x) ∨ (y = 1))

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Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.