A young student reported for a final examination
that consisted of only true/false questions. The
student took a seat in the hall, stared at the
test for five minutes, removed a coin from his
pocket and started tossing the coin and marking
the answer sheet. Heads meant true, tails meant
false. 

The young student finished the exam in 30
minutes, while the rest of the class was sweating
it out. Suddenly, during the last few minutes, the
young student began desperately throwing the coin
and sweating profusely. The moderator, alarmed,
approached the student and asked what was going
on. "Well, I finished the exam in half an hour,"
said the student, "but I thought I ought to
recheck my answers."