Let $X$ and $Y$ be two events such that $P(X \cup Y) = P(X) \cap P(Y)$. Statement 1: $P\left(X \cap…

Let $X$ and $Y$ be two events such that $P(X \cup Y) = P(X) \cap P(Y)$. Statement 1: $P\left(X \cap Y^{\prime}\right) = P\left(X^{\prime} \cap Y\right)$. Statement 2: $P(X) P(Y) = 2 P(X \cap Y)$.
  1. Statement 1 is false, Statement 2 is true.
  2. Statement 1 is true, Statement 2 is true, Statement 2 is not a correct explanation of Statement 1.
  3. Statement 1 is true, Statement 2 is false.
  4. Statement 1 is true, Statement 2 is true; Statement 2 is a correct explanation of Statement 1.

Solution

Let $X$ and $Y$ be two events such that $ P(X \cup Y)=P(X \cap Y) $ We know $ $\begin{aligned} & P(X \cup Y)=P(X)+P(Y)-P(X \cap Y) \\ & P(X \cap Y)=P(X)+P(Y)-P(X \cap Y) \\ & \text{(from }(1) \\ & \Rightarrow P(X)+P(Y)=2 P(X \cap Y) \end{aligned}$ $ Hence, Statement $-2$ is true. Now, $P\left(X \cap Y^{\prime}\right)=P(X)-P(X \cap Y)$ and $P\left(X^{\prime} \cap Y\right)=P(Y)-P(X \cap Y)$ This implies statement $-1$ is also true

Asked in: JEE Main 2012 (07 May Online)

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