Question

Let p,q,rp, q, r denote the statements “It is raining”, “It is cold”, and “It is pleasant”, respectively. Then the statement “It is not raining and it is pleasant, and it is not pleasant only if it is raining and it is cold” is represented by

Choose one option
Official answer and solution
Official answer
A
From
Official GATE 2017 answer key

Solution

Translate each component of the English compound sentence into propositional logic connectives.

Identify the propositional variables:

  • pp: “It is raining”
  • qq: “It is cold”
  • rr: “It is pleasant”

Deconstruct the sentence into its two main conjunctive parts:

  1. “It is not raining and it is pleasant”: ¬p∧r\neg p \wedge r.
  2. “and”: represented by the logical conjunction ∧\wedge.
  3. “it is not pleasant only if it is raining and it is cold”:
    In propositional logic, the conditional construction “AA only if BB” translates to A→BA \to B.
    Here, AA is “it is not pleasant” (¬r\neg r), and BB is “it is raining and it is cold” (p∧qp \wedge q).
    Therefore, “¬r\neg r only if (p∧q)(p \wedge q)” translates directly to ¬r→(p∧q)\neg r \to (p \wedge q).

Combining the two clauses with conjunction yields:

(¬p∧r)∧(¬r→(p∧q))(\neg p \wedge r) \wedge (\neg r \to (p \wedge q))

This corresponds to option A.

Final answer

A

Common trap

Confusing “A only if B” (A→BA \to B) with “A if B” (B→AB \to A).

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Source

Paper
GATE 2017 Computer Science and Information Technology (CS) Session 2
Question
11 of 65, printed as CS Q.11
Section
Computer Science and Information Technology

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