Question

What must be true in order for P (A or B) = P(A) + P (B)?

Answer 1

For the equation to be true, the events A and B must be mutually exclusive.

Answer 2

A and B must be disjoint in order for P (A or B) = P (A) + P (B). I am hoping that this answer has satisfied your query and it will be able to help you, and if you would like, feel free to ask another question.