What is Conditional Probability?
If A and B are any events in S (random experiment) then the probability of occurance of event A under the condition that B has already occurred and P(B) ≠ 0, is called the conditional probability.
It is denoted by 
Thus, we have = Probability of occurrence of A given that B has already occurred.
The meaning of symbols and 
depend on the nature of the events A and B and also the nature of the S experiment.
These 2 have following meaning:
= Probability of occurrence of A
When event B occurs or probability of occurrence of event A with respect to event B.
= Probability of occurrence of event B.
When event A occurs or probability of occurrence of event B with respect to event A.
So conditional probability of B relative to A is given by
