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JEE Main 201911 JanuaryMorning Shift
Exam
JEE Main
Year
2019
Date
11 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Mathematical Reasoning

JEE Main 2019 · 11 January · Morning Shift · Mathematics · Mathematical Reasoning

If q is false and p q rightarrow r is true, then which one of the...

If q\mathrm{q} is false and p∧q↔r\mathrm{p} \wedge \mathrm{q} \leftrightarrow \mathrm{r} is true, then which one of the following statements is a tautology?

Options

  1. A(p∨r)→(p∧r)(\mathrm{p} \vee \mathrm{r}) \rightarrow(\mathrm{p} \wedge \mathrm{r})
  2. B(p∧r)→(p∨r)\quad(\mathrm{p} \wedge \mathrm{r}) \rightarrow(\mathrm{p} \vee \mathrm{r})
  3. Cp∧r\mathrm{p} \wedge \mathrm{r}
  4. Dp∨r\mathrm{p} \vee \mathrm{r}

Correct answer

B. (p∧r)→(p∨r)\quad(\mathrm{p} \wedge \mathrm{r}) \rightarrow(\mathrm{p} \vee \mathrm{r})

Step-by-step solution

qisfalseandis false and[(p \wedge q) \leftrightarrow r]istrueAsis true As(p \wedge q)isfalseis false[False↔r]False \leftrightarrow r] is true Hence rr is false Option (1): says p∨rp \vee r, Since rr is false Hence (p∨r)(p \vee r) can either be true or false Option (2): says (p∧r)→(p∨r)(p∧r)(p \wedge r) \rightarrow(p \vee r) (p \wedge r) is false Since, F→TF \rightarrow T is true and F→FF \rightarrow F is also true Hence, it is a tautology Option (3): (p∨r)→(p∧r)(p \vee r) \rightarrow(p \wedge r) i.e. (p∨r)→F(p \vee r) \rightarrow F It can either be true or false Option (4): (p∧r)(p \wedge r) Since, rr is false Hence, (p∧r)(p \wedge r) is false.
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