Question

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 who does not have a sister has a brother?
Has a brother Does not have a brother
Has a sister 7 13
Does not have a sister 2 6

Answer 1

We want P(has brother | does not have sister) = (number with brother and no sister) / (total number with no sister) = 2 / (2+6) = 2/8 = 1/4 = 25%.