JEE Challenger
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Conditional Probability of Exhaustive Events and Given Event

Let H1,H2,…,HnH_1, H_2, \dots, H_n be mutually exclusive and exhaustive events with P(Hi)>0P(H_i) > 0, i=1,2,…,ni = 1, 2, \dots, n. Let EE be any other event with 0<P(E)<10 < P(E) < 1.

STATEMENT-1 : P(Hi∣E)>P(E∣Hi)⋅P(Hi)P(H_i \mid E) > P(E \mid H_i) \cdot P(H_i) for i=1,2,…,ni = 1, 2, \dots, n.
because
STATEMENT-2 : ∑i=1nP(Hi)=1\sum_{i=1}^n P(H_i) = 1.

Options

A

Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1

B

Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1

C

Statement-1 is True, Statement-2 is False

D

Statement-1 is False, Statement-2 is True

Correct

Step-by-Step Solution

To evaluate the given statements:

Evaluation of STATEMENT-2:
Since H1,H2,…,HnH_1, H_2, \dots, H_n are given to be mutually exclusive and exhaustive events, their union is the entire sample space SS, and they are pairwise disjoint. Therefore:
P(⋃i=1nHi)=∑i=1nP(Hi)=P(S)=1P\left(\bigcup_{i=1}^n H_i\right) = \sum_{i=1}^n P(H_i) = P(S) = 1
Hence, STATEMENT-2 is True.


Evaluation of STATEMENT-1:
By the definition of conditional probability:
P(Hi∣E)=P(Hi∩E)P(E)=P(E∣Hi)⋅P(Hi)P(E)P(H_i \mid E) = \frac{P(H_i \cap E)}{P(E)} = \frac{P(E \mid H_i) \cdot P(H_i)}{P(E)}

We are given that 0<P(E)<10 < P(E) < 1, which implies:
1P(E)>1\frac{1}{P(E)} > 1

However, EE is any event with 0<P(E)<10 < P(E) < 1. It is entirely possible that for some ii, the event EE and HiH_i are mutually disjoint, i.e., E∩Hi=∅E \cap H_i = \emptyset. In that case:
P(E∩Hi)=0  ⟹  P(E∣Hi)=0andP(Hi∣E)=0P(E \cap H_i) = 0 \implies P(E \mid H_i) = 0 \quad \text{and} \quad P(H_i \mid E) = 0

Substituting these values into the inequality:
P(Hi∣E)>P(E∣Hi)⋅P(Hi)  ⟹  0>0P(H_i \mid E) > P(E \mid H_i) \cdot P(H_i) \implies 0 > 0
which is mathematically false.

Therefore, the inequality does not necessarily hold for all i=1,2,…,ni = 1, 2, \dots, n.
Hence, STATEMENT-1 is False.


Conclusion:
Statement-1 is False, and Statement-2 is True.

Correct Option: (D)