If A and B are independent events such that 0 < P(A) < 1 and 0 < P(B) < 1, then identify the correct statements.
(A) A and B' are independent
(B) A' and B are independent
(C) A and B are mutually exclusive
(D) A' and B' are independent
Choose the correct answer from the options given below :
Answer & explanation
Correct answer: option 4
If A and B are independent then $P(A∩B)=P(A)P(B)$
now $P(A∩\overline{B})=P(A)−P(A∩B)=P(A)−P(A)P(B)$
$=P(A)\begin{Bmatrix}1−P(B)\end{Bmatrix}=P(A)P(\overline{B})$
Hence A and $\overline{B}$ are independent.
Similarly $P(\overline{A}∩\overline{B})=1−P(A∪B)=1−P(A)−P(B)+P(A∩B)$
$=1−P(A)−P(B)+P(A)P(B)=1−P(A)−P(B)\begin{Bmatrix}1−P(A)\end{Bmatrix}$
$=\begin{Bmatrix}1−P(A)\end{Bmatrix}\begin{Bmatrix}1−P(B)\end{Bmatrix}=P(\overline{A})P(\overline{B})$
Hence $\overline{A}$ and $\overline{B}$ are independent.
$P(\frac{A}{B})+P(\frac{\overline{A}}{B})=\frac{P(A∩B)}{P(B)}+\frac{P(\overline{A}∩B)}{P(B)}=P(A)+P(\overline{A})=1$
So, $P(A∩B) = P(A)P(B) = 0$ since $A/Q P(A) > 0$ and $P(B)>0$
A and B are not mutually exclusive.
So, A and B' are independent, A' and B are independent, A' and B' are independent
So option D is correct.