Question

In a math class with 27 students, a test was given the same day that an assignment was due. There were 20 students who passed the test and 21 students who completed the assignment. There were 18 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 assignment?

Answer 1

Let P = passed, A = completed. Then |P ∪ A| = 20 + 21 − 18 = 23, so 27 − 23 = 4 students did neither.

Probability = 4/27.