Multiplication rule and Addition rule

Multiplication rule

P(A and B) = P(AB) = P(A│B) x P(B) = P(B│A) x P(A)

Addition rule
The addition rule is used in situations that the probability of at least one of two events will occur.

P(A or B) = P(A) + P(B) - P(AB)

The sum P(A) + P(B) counts P(AB) twice, so a substraction is needed.

A joint probability of any number of independent events
Multiplication Rule for Independent Events:

P(A1A2….An) = P(A1)P(A2)….P(An)

Tips:

• Be remembered to deduct P(AB) once when applying the addition rule for dependent events.