Mrs. Jones surveys her class of 20 students about their siblings. In the class, 15 have a brother, 16 have a sister, and 12 have both a brother and a sister. What is the probability that a student has a brother OR a sister?
P(Brother or Sister) = .75 + .82 - .65 P(Brother or Sister) = .92 = 92% The reason you subtract the .65 is that scenario does not fit the rule. The rule is the probability of having a brother OR a sister. The .65 represents the kids who have both not either.
