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 brother has a sister?
Has a brother Does not have a brother
Has a sister 4 5
Does not have a sister 2 8

Answer 1

We want P(has sister | no brother) = (number with sister and no brother) / (total with no brother) = 5 / (5+8) = 5/13 ≈ 0.3846 (about 38.46%).