Question

8. You find the probability P(A or B) by using the equation PA or B) = P(A) + P(B) - P(A and B).

Answer 1

Step-by-step explanation:

When you add P(A) and P(B), the overlap P(A and B) is counted twice.  So you must subtract it to get the probability P(A or B).

If A and B are disjoint, then P(A and B) = 0, so it isn't necessary to subtract.