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.”