In a class of students, the following data table summarizes how many students have a brother or a sister. What is the probability that a student has a sister given that they have a brother?

Question

Has a brother	Does not have a brother
Has a sister	7	12
Does not have a sister	3	5

Answer 1

P(S|B) = P(S∩B)/P(B) = (7/27) / (10/27) = 7/10