Q. If $P(A) = P(B) = x\ and\ P(A \cap B) = P\left( A^{'} \cap B^{'} \right) = \frac{1}{3}$,then $x$ is equal to

A) $\frac{1}{2}$
B) $\frac{1}{4}$
C) $\frac{1}{3}$
D) $\frac{1}{6}$
Explanation

(a)
Given, $P(A) = P(B) = x$
and $P(A \cap B) = P\left( A^{'} \cap B^{'} \right) = \frac{1}{3}$
$\therefore\ P\left( A^{'} \cap B^{'} \right) = 1 - P(A \cup B)$
$\Rightarrow \ P(A \cup B) = 1 - \frac{1}{3} = \frac{2}{3}$ …(i)
Also, $P(A \cup B) = P(A) + P(B) - P(A) \cap B)$
$\Rightarrow \ \frac{2}{3} = 2x - \frac{1}{3}$ [from Eq (i)]
$\Rightarrow \ x = \frac{1}{2}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

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