3. The Addition Law

P(A?B) = P(A) + P(B) - P(A?B)

It’s important to subtract the intersection (overlap) because we can’t add that area twice.

For events that are mutually exclusive, there is no intersection, and the joint probability P(A?B)=0. Thus the addition law boils down to:

P(A?B) = P(A) + P(B)

Previous slide

Next slide

Back to first slide

View graphic version