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JEE Main 2024
Mathematical Reasoning
Mathematical Reasoning
Easy

Question

Consider the following statements: A : Rishi is a judge. B : Rishi is honest. C : Rishi is not arrogant. The negation of the statement "if Rishi is a judge and he is not arrogant, then he is honest" is

Options

Solution

Key Concepts and Formulas

  • Implication: The implication PQP \to Q is equivalent to PQ\sim P \lor Q.
  • Negation of Implication: The negation of PQP \to Q is PQP \land \sim Q.
  • De Morgan's Laws: (PQ)PQ\sim (P \land Q) \equiv \sim P \lor \sim Q and (PQ)PQ\sim (P \lor Q) \equiv \sim P \land \sim Q.

Step-by-Step Solution

Step 1: Express the given statement in symbolic form. The given statement "if Rishi is a judge and he is not arrogant, then he is honest" can be written as (AC)B(A \land C) \to B. We are given that A: Rishi is a judge, B: Rishi is honest, and C: Rishi is not arrogant.

Step 2: Find the negation of the statement. We need to find the negation of (AC)B(A \land C) \to B. Using the negation of implication formula, (PQ)PQ\sim (P \to Q) \equiv P \land \sim Q, we have: ((AC)B)(AC)B\sim ((A \land C) \to B) \equiv (A \land C) \land \sim B.

Step 3: Rewrite the negation to match the options. We have the negation as (AC)B(A \land C) \land \sim B. Now, we need to manipulate this expression to see if we can arrive at one of the options. We can rewrite this as B(AC)\sim B \land (A \land C). This expression matches option (B). However, we are given that the correct answer is (A). This means that there must be an error in the question or the provided correct answer. Let us explore the other options to see if they are equivalent to the derived answer.

Option (A) is B(AC)B \to (A \lor C). The negation of this is B(AC)B(AC)B \land \sim (A \lor C) \equiv B \land (\sim A \land \sim C). This is not equal to B(AC)\sim B \land (A \land C).

Option (C) is B(AC)B \to (\sim A \lor \sim C). The negation of this is B(AC)B(AC)B \land \sim (\sim A \lor \sim C) \equiv B \land (A \land C). This is not equal to B(AC)\sim B \land (A \land C).

Option (D) is B(AC)B \to (A \land C). The negation of this is B(AC)B(AC)B \land \sim (A \land C) \equiv B \land (\sim A \lor \sim C). This is not equal to B(AC)\sim B \land (A \land C).

Our derived negation is B(AC)\sim B \land (A \land C). Since we're told the correct answer is option (A), which is B(AC)B \to (A \lor C), let's find the negation of option (A) and see if it matches our derived negation: (B(AC))=(B(AC))=B(AC)=B(AC)\sim (B \to (A \lor C)) = \sim (\sim B \lor (A \lor C)) = B \land \sim(A \lor C) = B \land (\sim A \land \sim C). This does not match our derived negation.

Since the correct answer is (A) which is B(AC)B \to (A \vee C), then the original statement must be equivalent to the negation of (A). The negation of (A) is (B(AC))=B(AC)=B(AC)\sim(B \to (A \vee C)) = B \wedge \sim (A \vee C) = B \wedge (\sim A \wedge \sim C). Therefore, the original statement must be (B(AC))\sim(B \wedge (\sim A \wedge \sim C)). (B(AC))=B(AC)\sim(B \wedge (\sim A \wedge \sim C)) = \sim B \vee (A \vee C). We are given the original statement is (AC)B(A \wedge C) \to B, which is equivalent to (AC)B(AC)BBAC\sim (A \wedge C) \vee B \equiv (\sim A \vee \sim C) \vee B \equiv B \vee \sim A \vee \sim C. Since B(AC)\sim B \vee (A \vee C) is not equivalent to (AC)B(\sim A \vee \sim C) \vee B, there must be an error in the question or the provided correct answer.

Going back to the original derivation, the negation of (AC)B(A \wedge C) \to B is (AC)B(A \wedge C) \wedge \sim B, which is equivalent to B(AC)\sim B \wedge (A \wedge C). This matches option (B).

Common Mistakes & Tips

  • Be careful while applying the negation of an implication. Remember (PQ)PQ\sim (P \to Q) \equiv P \land \sim Q.
  • Double-check the application of De Morgan's Laws.
  • When given multiple options, simplify the expression to match one of the options.

Summary

The given statement is (AC)B(A \wedge C) \to B. The negation of this statement is (AC)B(A \wedge C) \wedge \sim B, which can be written as B(AC)\sim B \wedge (A \wedge C). Based on the given options, the answer is B(AC)\sim B \wedge (A \wedge C). However, the listed correct answer is option (A). Since the derived answer does not match the negation of option (A), there must be an error in the question or the provided correct answer. The correct answer should be option (B).

Final Answer

The final answer is \boxed{\sim B \wedge (A \wedge C)}, which corresponds to option (B).

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