MCQ
For any two events $A$ and $B$ in a sample space
  • $P\,\left( {\frac{A}{B}} \right) \ge \frac{{P(A) + P(B) - 1}}{{P(B)}},\,\,P(B) \ne 0$ is always true
  • B
    $P\,(A \cap \bar B) = P(A) - P(A \cap B)$ does not hold
  • C
    $P\,(A \cup B) = 1 - P(\bar A)\,P(\bar B),$ if $A$ and $B$ are disjoint
  • D
    None of these

Answer

Correct option: A.
$P\,\left( {\frac{A}{B}} \right) \ge \frac{{P(A) + P(B) - 1}}{{P(B)}},\,\,P(B) \ne 0$ is always true
a
(a) We know that $P(A/B) = \frac{{P(A \cap B)}}{{P(B)}}$

Also we know that $P(A \cup B) \le 1$

$ \Rightarrow P(A) + P(B) - P(A \cap B) \le 1$

$ \Rightarrow P(A \cap B) \ge P(A) + P(B) - 1$

$ \Rightarrow \frac{{P(A \cap B)}}{{P(B)}} \ge \frac{{P(A) + P(B) - 1}}{{P(B)}}$

$ \Rightarrow P(A/B) \ge \frac{{P(A) + P(B) - 1}}{{P(B)}}$

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