In a math class with 20 students, a test was given the same day that an assignment was due. There were 11 students who passed the test and 15 students who completed the assignment. There were 9 students who passed the test and also completed the assignment. What is the probability that a student chosen randomly from the class failed the test and did not complete the homework?

1 answer

number(passed or handed in assignment)
= 11 + 15 - 9
= 17
but there were 20 students, so we have 3 failed and did not hand in assignment

You can get the same result by using a Venn diagram