The Final Exam.......

At Penn State University, there were four sophomores
taking chemistry and all of them had an 'A' so far. These
four friends were so confident that the weekend before
finals, they decided to visit some friends and have a big party.
They had a great time but, after all the hearty partying, they
slept all day Sunday and didn't make it back to Penn State
until early Monday morning.

Rather than taking the final then, they decided that after the
final they would explain to their professor why they missed
it. They said that they visited friends but on the way back
they had a flat tire. As a result, they missed the final. The
professor agreed they could make up the final the next day.
The guys were excited and relieved. They studied that night
for the exam.

The next day the Professor placed them in separate rooms
and gave them a test booklet. They quickly answered the
first problem worth 5 points. Cool, they thought! Each one in
separate rooms, thought this was going to be easy..... then
they turned the page. On the second page was written.....

For 95 points: Which tire? _________