If $A$ and $B$ are such events that $P(A) > 0$ and $P(B) \neq 1$, then $P(A' \mid B')$ is equal to

$\frac{1 - P(A \cup B)}{P(B')}$

The correct answer is Option (3) → $\frac{1 - P(A \cup B)}{P(B')}$ ##

$∵P(A) > 0$ and $P(B) \neq 1$

$∴P(A' \mid B') = \frac{P(A' \cap B')}{P(B')} = \frac{P(A \cup B)'}{P(B')} = \frac{1 - P(A \cup B)}{P(B')}$