Conditional Probability

1. Oct 19, 2009

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.