Q. $If\ A\ and\ B\ are\ independent\ events\ of\ a\ random\ experiments\ such\ that$ $P(A \cap B) = \frac{1}{6}and\ P\left( \overline{A} \cap \overline{B} \right) = \frac{1}{3},\ then\ P(A)\ is\ equal\ to$

A) $\frac{1}{4}$
B) $\frac{1}{3}$
C) $\frac{5}{7}$
D) $\frac{2}{3}$
Explanation

(b)
Since, $A\ and\ B\ are\ independent\ events$
$\therefore P(A)P(B) = \frac{1}{6}\ and\ P\left( \overline{A} \right)P\left( \overline{B} \right) = \frac{1}{3}$
$\Rightarrow \ \left\lbrack 1 - P(A) \right\rbrack\left\lbrack 1 - P(B) \right\rbrack = \frac{1}{3}$
$\Rightarrow \ 1 - \left\lbrack P(A) + P(B) \right\rbrack + P(A)P(B) = \frac{1}{3}$
$\Rightarrow \ 1 + \frac{1}{6} - \frac{1}{3} = P(A) + P(B)$
$\Rightarrow \ P(A) + P(B) = \frac{5}{6}$
$\Rightarrow \ P(A) = \frac{1}{2}\ ,\ P(B) = \frac{1}{3}\ ,\$
$or\ P(A) = \frac{1}{3}\ ,\ P(B) = \frac{1}{2}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

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