At Duke University, four sophomores were taking Organic Chemistry.  They did so well on all the quizzes, midterms and labs that each had an A as they headed into the final exam. The four friends were so confident that the weekend before finals, they decided to go up to University of Virginia for a party.

The Dukies had a grand time, but after all of the partying they were exhausted and didn’t make it back to campus in time for the final. They approached their professor and explained that they had gone to UVA for the weekend with the plan to come home early to study. Unfortunately, on the drive home, their car had a flat; and since they didn’t have a spare and couldn't get help for a long time, they were delayed in their return.

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 and handed each of them a test booklet.  The first problem was a snap: something about the formation of free radicals. Then, each in his own room, turned the page. 

On the second page was written…

"For 95 points:  Which tire?"