Q. If $A$ and $B$ are mutually exclusive events with $P(A) = \frac{1}{2} \times P(B)and\ A \cup B = S$,(total sample space) then $P(A)$ is equal to

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

(b)
Given, $A \cup B = S$
$\therefore P(A \cup B) = P(S) = 1$
$\Rightarrow P(A) + P(B) = 1\ \ \ \ \ \lbrack\because P(A \cap B) = 0\rbrack$
$\Rightarrow P(A) + 2P(A) = 1$
$\Rightarrow P(A) = \frac{1}{3}\ \ \ \ \lbrack\because P(B) = 2P(A),\ given\rbrack$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

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