Question

n a class of students, the following data table summarizes how many students passed a test and completed the homework due the day of the test. What is the probability that a student failed the test given that they completed the homework?
Passed the test Failed the test
Completed the homework 21 3
Did not complete the homework 2 4

Answer 1

We want P(failed | completed) = (# who completed and failed) / (total who completed) = 3 / (21 + 3) = 3/24 = 1/8 = 0.125 = 12.5%.