Q. It is given the events $A$ and $B$ are such that $P(A) = \frac{1}{4},P\left( A \middle| B \right) = \frac{1}{2}and\ P\left( B \middle| A \right) = \frac{2}{3}$.Then, $P(B)$ is

A) $\frac{1}{2}$
B) $\frac{1}{6}$
C) $\frac{1}{3}$
D) $\frac{2}{3}$
Explanation

(c)
We know, $P\left( \frac{A}{B} \right) = \frac{P(A \cap B)}{P(B)}$
and $P\left( \frac{B}{A} \right) = \frac{P(B \cap A)}{P(A)}$
$\therefore P(B) = \frac{P\left( \frac{B}{A} \right).P(A)}{P\left( \frac{A}{B} \right)}$
$= \frac{\left( \frac{2}{3} \right)\left( \frac{1}{4} \right)}{\left( \frac{1}{2} \right)} = \frac{1}{3}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.