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JEE Main 2022
Mathematical Reasoning
Mathematical Reasoning
Easy

Question

The converse of ((p)q)r((\sim p) \wedge q) \Rightarrow r is

Options

Solution

Key Concepts and Formulas

  • Converse of a Conditional Statement: The converse of a statement pqp \Rightarrow q is qpq \Rightarrow p.
  • Conditional Statement as Disjunction: pqp \Rightarrow q is logically equivalent to (p)q(\sim p) \vee q.
  • De Morgan's Laws: (pq)(p)(q)\sim (p \wedge q) \equiv (\sim p) \vee (\sim q) and (pq)(p)(q)\sim (p \vee q) \equiv (\sim p) \wedge (\sim q).

Step-by-Step Solution

Step 1: State the given conditional statement.

We are given the statement ((p)q)r((\sim p) \wedge q) \Rightarrow r.

Step 2: Find the converse of the given statement.

The converse of a statement pqp \Rightarrow q is qpq \Rightarrow p. Therefore, the converse of ((p)q)r((\sim p) \wedge q) \Rightarrow r is r((p)q)r \Rightarrow ((\sim p) \wedge q).

Step 3: Express the converse as a disjunction.

We know that pqp \Rightarrow q is equivalent to (p)q(\sim p) \vee q. Thus, r((p)q)r \Rightarrow ((\sim p) \wedge q) is equivalent to (r)((p)q)(\sim r) \vee ((\sim p) \wedge q).

Step 4: Manipulate the expression to match one of the given options.

We have (r)((p)q)(\sim r) \vee ((\sim p) \wedge q). Our target is option (C), which is (p(q))(r)(p \vee (\sim q)) \Rightarrow (\sim r). Let's convert this option into a disjunction: ((p(q)))(r)(\sim (p \vee (\sim q))) \vee (\sim r).

Now let's simplify the negation using De Morgan's Law: (p(q))(r)(\sim p \wedge \sim(\sim q)) \vee (\sim r), which becomes (pq)(r)(\sim p \wedge q) \vee (\sim r).

This is precisely what we have derived in Step 3: (r)((p)q)(\sim r) \vee ((\sim p) \wedge q). Therefore, the converse is equivalent to ((p(q)))(r)(\sim (p \vee (\sim q))) \vee (\sim r), which is the same as (p(q))(r)(p \vee (\sim q)) \Rightarrow (\sim r).

Step 5: Write out the final form of the converse.

The converse of ((p)q)r((\sim p) \wedge q) \Rightarrow r is r((p)q)r \Rightarrow ((\sim p) \wedge q), which is equivalent to (r)((p)q)(\sim r) \vee ((\sim p) \wedge q). Further simplification gives ((p)q)(r)((\sim p) \wedge q) \vee (\sim r), and finally (p(q))(r)(p \vee (\sim q)) \Rightarrow (\sim r).

Common Mistakes & Tips

  • Confusing Converse, Inverse, and Contrapositive: Make sure to remember the definitions of each. The converse switches the hypothesis and conclusion. The inverse negates both. The contrapositive switches and negates both.
  • Applying De Morgan's Laws Correctly: Be careful with the negations when applying De Morgan's laws. (pq)=(p)(q)\sim (p \wedge q) = (\sim p) \vee (\sim q) and (pq)=(p)(q)\sim (p \vee q) = (\sim p) \wedge (\sim q).
  • Using pqpqp \Rightarrow q \equiv \sim p \vee q: This equivalence is very useful for simplifying conditional statements.

Summary

We started with the given statement ((p)q)r((\sim p) \wedge q) \Rightarrow r and found its converse, r((p)q)r \Rightarrow ((\sim p) \wedge q). We then used the equivalence pq(p)qp \Rightarrow q \equiv (\sim p) \vee q to express the converse as a disjunction. Applying De Morgan's Law and converting back to a conditional statement, we arrived at (p(q))(r)(p \vee (\sim q)) \Rightarrow (\sim r), which corresponds to option (C).

Final Answer

The final answer is \boxed{(p \vee (\sim q)) \Rightarrow (\sim r)}, which corresponds to option (C).

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