Answered By Leonardo F

The additive principle states that if a certain event A can occur in m ways and event B can occur n ways and the two events are disjoint, then the number of ways for A or B to occur will be m+n. In terms of probability:

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

If the two events cannot happen at the same time (also called mutually exclusive or disjoint), then:

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