Chemisty Exam

A lesson to be learned!
At Duke 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.
They had a great time, but after all the fun, they
slept all day Sunday and
didn't make it back to Duke 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 Professor placed them in separate rooms and
gave them each a test
booklet.
Each quickly answered the first problem worth 5
points. Cool, they thought!
Each one in separate rooms, thinking this was
going to be Easy.... then
they turned the page. On the second page was
written....
For 95 points: Which tire? _____