**Complementary event or â€˜not eventâ€™** : The set Aâ€² or S â€“ AÂ

**Event A or B:** The set A âˆª B

**Event A and B:** The set A âˆ© B

**Event A and not B:** The set A â€“ B

**Mutually exclusive event:** A and B are mutually exclusive if A âˆ© B = Ï†

**Equally likely outcomes:** All outcomes with equal probability

**Probability of an event:** For a finite sample space with equally likely outcomes

Probability of an event \( P(A) = \frac{n(A)}{n(S)} \), where n(A) = number of elements in the set A,

n(S) = number of elements in the set S.

If A and B are any two events, then

P(A or B) = P(A) + P(B) â€“ P(A and B) equivalently,

P(A âˆª B) = P(A) + P(B) â€“ P(A âˆ© B)

If A and B are mutually exclusive, then P(A or B) = P(A) + P(B)

If A is any event, then P(not A) = 1 â€“ P(A)