Probability of combination of events
Union of events: If A and B are two events of the sample space S then A U B or A+B is a union of events and is the event that either A or B or both take place.
Intersection of events: If A and B are two events of the sample space S, the A ∩ B or AB is an intersection of events is the event that both A and B take place.
Mutually Exclusive events: Two events A and B of the sample space S are said to be mutually exclusive events if they cannot occur simulataneously. If A occurs B does not occur or if B occurs A does not occur.
It means A ∩ B , the event that both will occur is a null set.
Exhausive events: If two events A and B of a sample space are said to be exhausive events, if A U B contains all the points of the sample space.
Theorem regarding combination of events
If A and B are two events of sample space S, then
P(A U B) = P(A) + P(B) - P(A ∩ B)