# Math Help - Help probability question

1. ## Help probability question

This is probably a simple question but I can't get it
P(A)=0.5 and P(AuB)=0.6, find P(B) if A and B are independent

2. Originally Posted by Happy Dancer
This is probably a simple question but I can't get it
P(A)=0.5 and P(AuB)=0.6, find P(B) if A and B are independent
A and B are independent so $P(A \cup B)=P(A)+P(B)-P(A)B(B)$.
Now solve for $P(B)$.

3. Thanks, btw I have another problem. Find P(B) given that P(A|B)=0.4
P(B)=P(AnB)/P(A|B)=P(A)P(B)/P(A|B)
so P(B)=1.25 P(B)
How can this be right?

4. Originally Posted by Happy Dancer
Thanks, btw I have another problem. Find P(B) given that P(A|B)=0.4
P(B)=P(AnB)/P(A|B)=P(A)P(B)/P(A|B)
so P(B)=1.25 P(B)
How can this be right? What you have done is not correct!
You must have been given some information about $P(A)$.

5. Yes, carrying on from the previous question P(A)=0.5

6. Originally Posted by Happy Dancer
Yes, carrying on from the previous question P(A)=0.5
If A & B are independent then $P(A)=0.4 \ne 0.5$!
So there is a mistake in the problem.

Why not post the exact question.