# Conditional probability question

• Sep 3rd 2009, 03:22 PM
Danneedshelp
Conditional probability question
Q: If two events, A and B, are such that P(A)=0.5, P(B)=0.3, and P(A intersection B)=0.1, find the following:

1) P(A|A union B)

2) P(A|A intersection B)

I keep getting the wrong result when I use the conditional probability formula. I think it is because A and B are dependent events and I am not sure how to treat them.
• Sep 3rd 2009, 04:00 PM
Plato
Quote:

Originally Posted by Danneedshelp
Q: If two events, A and B, are such that P(A)=0.5, P(B)=0.3, and P(A intersection B)=0.1, find the following:
1) P(A|A union B)
2) P(A|A intersection B)

First: $P(A \cup B)=0.5+0.3-0.1=0.7~,~A\cap(A\cup B)=A~,\&~A\cap(A\cap B)=(A\cap B)$

Now $P(K|J)=\frac{P(K\cap J)}{P(J)}$