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 12 5
Does not have a sister 10 2

Answer 1

We want P(has a brother | does not have a sister) = (# without sister who have a brother) / (total # without sister) = 10 / (10+2) = 10/12 = 5/6 ≈ 83.3%.