The following situation is from a Marilyn vos Savant column in the Sunday Parade. Is she right or is she wrong? Be sure you can defend your answer!


"Suppose it is assumed that about 5% of the general population uses drugs. Assume further that you employ a drug test that is 95% accurate*.

A person is selected at random and given the test. The test is positive. What does such a result suggest? Would you conclude that the individual is highly likely to be a drug user?"

Here is Marilyn’s answer: "Given the conditions, once a person has tested positive, you may as well flip a coin to determine whether he or she is a drug user. The chances are 50-50."



Work on this project in pairs. Be ready to do two things by tomorrow’s class (3/2/00):

  1. Each person will submit a 1-2 page report of their thinking about the problem. You are expected to write legibly, in full and grammatically correct sentences, and to say thoughtful things about how you reasoned through the problem and how you solved it. Your report may include comments about any difficulties you may have experienced, but it must address the questions and issues raised in the problem in a way that demonstrates and communicates your understanding of them. You are encouraged to use diagrams to help the reader understand your reasoning.

(2) Present your reasoning and solution in class for discussion. Aim to give a clear explanation of your thinking so that others can understand it.