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JEE Main 2024
Mathematical Reasoning
Mathematical Reasoning
Easy

Question

Consider the following statements: P : Ramu is intelligent. Q : Ramu is rich. R : Ramu is not honest. The negation of the statement "Ramu is intelligent and honest if and only if Ramu is not rich" can be expressed as:

Options

Solution

Key Concepts and Formulas

  • Biconditional Equivalence: AB(AB)(BA)(AB)(BA)A \Leftrightarrow B \equiv (A \Rightarrow B) \wedge (B \Rightarrow A) \equiv (\sim A \vee B) \wedge (\sim B \vee A)
  • Negation of Biconditional: (AB)(AB)(BA)\sim (A \Leftrightarrow B) \equiv (A \wedge \sim B) \vee (B \wedge \sim A)
  • De Morgan's Laws:
    • (AB)AB\sim (A \wedge B) \equiv \sim A \vee \sim B
    • (AB)AB\sim (A \vee B) \equiv \sim A \wedge \sim B

Step-by-Step Solution

Step 1: Translate the given statement into symbolic form.

The statement "Ramu is intelligent and honest if and only if Ramu is not rich" can be written as: (PR)Q(P \wedge \sim R) \Leftrightarrow \sim Q We are given that PP represents "Ramu is intelligent," QQ represents "Ramu is rich," and RR represents "Ramu is not honest." Therefore, R\sim R represents "Ramu is honest," and Q\sim Q represents "Ramu is not rich."

Step 2: Find the negation of the statement.

We need to find the negation of (PR)Q(P \wedge \sim R) \Leftrightarrow \sim Q, which is [(PR)Q]\sim[(P \wedge \sim R) \Leftrightarrow \sim Q].

Step 3: Apply the negation of the biconditional equivalence.

Using the formula (AB)(AB)(BA)\sim (A \Leftrightarrow B) \equiv (A \wedge \sim B) \vee (B \wedge \sim A), we have: [(PR)Q][(PR)(Q)][Q(PR)]\sim[(P \wedge \sim R) \Leftrightarrow \sim Q] \equiv [(P \wedge \sim R) \wedge \sim (\sim Q)] \vee [\sim Q \wedge \sim (P \wedge \sim R)]

Step 4: Simplify the expression.

Since (Q)Q\sim (\sim Q) \equiv Q, we have: [(PR)Q][Q(PR)][(P \wedge \sim R) \wedge Q] \vee [\sim Q \wedge \sim (P \wedge \sim R)]

Step 5: Apply De Morgan's Law.

Using De Morgan's Law, (PR)P(R)PR\sim (P \wedge \sim R) \equiv \sim P \vee \sim (\sim R) \equiv \sim P \vee R. Thus, the expression becomes: [(PR)Q][Q(PR)][(P \wedge \sim R) \wedge Q] \vee [\sim Q \wedge (\sim P \vee R)]

Step 6: Compare the result with the given options.

The expression we obtained is ((PR)Q)((Q)((P)R))((P \wedge \sim R) \wedge Q) \vee ((\sim Q) \wedge ((\sim P) \vee R)). This matches option (A).

Common Mistakes & Tips

  • Remember to use De Morgan's Laws correctly when negating conjunctions or disjunctions.
  • Be careful with the negation of negations (e.g., (Q)=Q\sim (\sim Q) = Q).
  • When translating statements into symbolic form, pay close attention to the meaning of each variable and its negation.

Summary

We first translated the given statement into symbolic form as (PR)Q(P \wedge \sim R) \Leftrightarrow \sim Q. Then we found the negation of this statement using the negation of the biconditional equivalence and De Morgan's laws. After simplifying the expression, we obtained ((PR)Q)((Q)((P)R))((P \wedge \sim R) \wedge Q) \vee ((\sim Q) \wedge ((\sim P) \vee R)), which corresponds to option (A).

Final Answer

The final answer is \boxed{((P \wedge(\sim R)) \wedge Q) \vee((\sim Q) \wedge((\sim P) \vee R))}, which corresponds to option (A).

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