In all above, P (A $\cap$ B) is the probability of simultaneous occurrence of two events A and B, P (A) is the probability of the occurrence of first event, P (B) and P (B | A) is the probability of second event if events are independent or dependent respectively. P (B| A) is read as the probability of occurrence of event B when event A has already taken place. Also, P (B) = P (B | A) if the events are dependent and if events are independent then P (B | A) = P (B).

In general we can use the formula **P (A**** $\cap$ B) = P (A) P (B | A)**

Depending upon the dependency of the event we can use it either ways as explained above.

It is important to note that intersection of two complement events is always equal to zero. This is because if A is an event, then A’ is the complement of event A. It is clear that A $\cap$ A’ = Null. This implies **P (A $\cap$ A’) = 0**