These four guys were enrolled in an Organic Chemistry class at USC. They did so well on all the quizzes, midterms and labs, that each had an "A" for the semester. These guys were so confident that they decided to go up to Stanford and party with some friends the weekend before finals. After all the hardy-partying, they slept all day Sunday and didn`t make it back to USC until Monday morning. Since they were late for the final, they decided to make an excuse to the professor so they could take a make-up exam. Later on in the day, they found their professor and explained that they had gone to Stanford for the weekend, but, unfortunately, they had a flat tire on the way back, didn`t have a spare, and couldn`t get help for a long time. As a result, they missed the final.

           The Professor thought it over and then agreed they could make up the final the following day. The guys were elated and relieved. They studied that night and went in the next day at the time the professor had told them.

           He placed them in separate rooms, handed each of them a test booklet, and told them to begin.

           They looked at the first problem, worth 5 points, something simple about free radical formation. "Cool," they thought at the same time, each one in his separate room, "this is going to be easy."

Each finished the problem and then turned the page. On the second page was written:

(For 95 points): Which tire?