Bayes theorem

For any two events A and B, with $\mathbb{P}(B)>0$, we define the conditional probability of A given B ($\mathbb{P}(A|B)$) as $$\mathbb{P}(A|B)=\frac{\mathbb{P}(A\cap B)}{\mathbb{P}(B)}$$ Example: We throw a dice once, and it lands on an even number.