ProbabilityHardBloom L3
Question
Let $A,B$ be independent events with $P(A) = P(B)$ and $P(A \cup B) = \frac{1}{2}$, then $P(A)$ is equal to
Options
A.$1 - \frac{1}{\sqrt{2}}$
B.$\frac{1}{\sqrt{2}}$
C.$\sqrt{2} - 1$
D.$2 - \sqrt{2}$
Solution
Sol. [Key Concept: $A,B$ independent, $P(A) = P(B)$, given $P(A \cup \ B)$: solve for $P(A)$.]
$$P(A \cup B) = P(A) + P(B) - P(A \cap B)$$
$$\begin{matrix} \Rightarrow & \frac{1}{2} = 2P(\text{ }A) - (P(\text{ }A))^{2} \\ \Rightarrow & P(\text{ }A) = 1 - \frac{1}{\sqrt{2}} \end{matrix}$$
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