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If $P\left(A^{\prime}\right)=0 \cdot 6, P(B)=0 \cdot 8$ and $P(B / A)=0 \cdot 3$, then $P(A / B)=$
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The correct answer is:
$\frac{3}{20}$
Given $P\left(A^{\prime}\right)=0.6 \Rightarrow P(A)=1-0.6=0.4, P(B)=0.8, P(B / A)=0.3$
We know that $\mathrm{P}(\mathrm{B} / \mathrm{A})=\frac{\mathrm{P}(\mathrm{A} \cap \mathrm{B})}{\mathrm{P}(\mathrm{A})}$ and $\mathrm{P}(\mathrm{A} / \mathrm{B})=\frac{\mathrm{P}(\mathrm{A} \cap \mathrm{B})}{\mathrm{P}(\mathrm{B})}$
Here $P(A \cap B)=P(A) \cdot P(B / A)=(0.4)(0.3)=0.12$
Also $\quad P(A \cap B)=P(A / B) \cdot P(B)$
$\therefore \mathrm{P}(\mathrm{A} / \mathrm{B})=\frac{0.12}{0.8}=\frac{12}{80}=\frac{3}{20}$
We know that $\mathrm{P}(\mathrm{B} / \mathrm{A})=\frac{\mathrm{P}(\mathrm{A} \cap \mathrm{B})}{\mathrm{P}(\mathrm{A})}$ and $\mathrm{P}(\mathrm{A} / \mathrm{B})=\frac{\mathrm{P}(\mathrm{A} \cap \mathrm{B})}{\mathrm{P}(\mathrm{B})}$
Here $P(A \cap B)=P(A) \cdot P(B / A)=(0.4)(0.3)=0.12$
Also $\quad P(A \cap B)=P(A / B) \cdot P(B)$
$\therefore \mathrm{P}(\mathrm{A} / \mathrm{B})=\frac{0.12}{0.8}=\frac{12}{80}=\frac{3}{20}$
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