# Thread: Probability of Independent Events

1. ## Probability of Independent Events

Hi,

If hypothetical events A and B are independent, with P(B/A)=.4, and P(A)=.3

What is the P(B)? What formula would you use to figure this out?

Thanks.

2. ## Re: Probability of Independent Events

Hi! We are glad that you posted here! This looks like a homework question though. Our homework help policy can be found here. We mainly just want to see what you have tried so far and that you have put some effort into the problem. I would also suggest checking out this thread for some guidelines on smart posting behavior that can help you get answers that are better much more quickly.

3. ## Re: Probability of Independent Events

P(B/A)=P(A intersection B)/P(A)?

am I on the right track?

4. ## Re: Probability of Independent Events

It's certainly a start. What do you know about if A and B are independent?

5. ## Re: Probability of Independent Events

P(A intersection B) cannot exist if A and B are independent.

6. ## Re: Probability of Independent Events

Not quite true. If A and B are mutually exclusive then P(A intersect B) = 0. However, mutually exclusive and independent aren't the same thing. Maybe you want to go back and look at what you have for the definition of independent?

7. ## Re: Probability of Independent Events

Well if they are independent, than by definition P(B/A) has to equal P(B), thus P(B) also equals .4?

8. ## Re: Probability of Independent Events

That's certainly one way to do it.

9. ## Re: Probability of Independent Events

lol. so in conclusion if P(A)=.3, P(B)=.4, than P(B/A)=.4 ?

thanks.

10. ## Re: Probability of Independent Events

To set formal definitions: and .

We then have , then .

By the independence of A and B, .