Calculating Conditional Probability: A and B Events with A' and B' Notation

[Homewoodm01]

An event A has a 70% chance of occurring, an event B has a 40% of occurring and the event (A n B) has a 20% chance of occurring. The events are not unrelated.

If A does not occur what is the probability of B?

notation A' means (not A)

I have tried to use the formula P(B|A') = P(B n A')/P(A')


However Not sure if that's the right way to go and if A' would be equal to .3.

Please Help :)

 

[honestrosewater]

Yes, P(A') = 1 - P(A). Have you heard of http://en.wikipedia.org/wiki/Bayes'_theorem#Alternative_forms"?

 

[Homewoodm01]

Thanks for the link, I have used one of Baye's laws hopefully that helps give me the right answer.