Probability Question 267

Question: $ P(A\cup B)=P(A\cap B) $ if and only if the relation between $ P(A) $ and $ P(B) $ is

[IIT 1985]

Options:

A) $ P(A)=P(\bar{A}) $

B) $ P(A\cap B)=P(A’\cap B’) $

C) $ P(A)=P(B) $

D) None of these

Show Answer

Answer:

Correct Answer: C

Solution:

$ P(A)=P(B) $

As this gives $ P(A\cup B)=P(A)+P(B)-P(A\cap B) $ or $ P(A)=2P(A)-P(A) $
$ \Rightarrow P(A\cup B)=P(A\cap B). $