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Need solution for RD sharma maths class 12 chapter 30 probablity exercise Very short answer question, question 13

Answers (1)

Answer : \frac{1}{4}

Hint:

\begin{aligned} &P\left(\frac{B}{A \cup B^{\prime}}\right)=\frac{P\left(B \cap\left(A \cup B^{\prime}\right)\right)}{P\left(A \cup B^{\prime}\right)} \\ \end{aligned}

Given:

\begin{aligned} &P\left(A^{\prime}\right)=0.3 \\ &P(B)=0.4 \end{aligned} and

\begin{aligned} P\left(A \cap B^{\prime}\right)=0.5 \end{aligned} Then

Explanation:

We have

\begin{aligned} &P(\bar{A})=0.3, P(B)=0.4\end{aligned}  and \begin{aligned}& P(A \cap \bar{B})=0.5 \end{aligned}

According to bay’s theorem

\begin{aligned} P\left(\frac{B}{A \cap \bar{B}}\right)=\frac{P(B \cap(\bar{A} \cap \bar{B}))}{P(\bar{A} \cap \bar{B})}\\ =\frac{P(B \cap(\overline{A \cup B}))}{P(\bar{A} \cap \bar{B})} \end{aligned}

                           \begin{aligned} =\frac{P(\bar{B} \cap(\overline{A \cup B}))}{P(\bar{A} \cap \bar{B})}\\ =\frac{P(\bar{B} \cup(A \cup B))}{P(\bar{A} \cap \bar{B})} \end{aligned}

Now

\begin{aligned} \bar{B} \cup B=U=\phi \end{aligned}  Where U=universal set

So

\begin{aligned} P(\bar{B} \cup(A \cup B))=\phi \end{aligned}

Therefore \begin{aligned} P\left(\frac{B}{\bar {A} \cap \bar{B}}\right)=0 \end{aligned}

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