A blonde student sits for her university final exam, which consists mainly of true-or-false questions. She stares at the test paper for five minutes, then has an idea. She takes a coin from her purse and begins tossing it to determine her answers: heads for true, tails for false.
Within thirty minutes, she finishes while the rest of the class is still working hard. In the final minutes, however, she is seen desperately tossing the coin again, swearing and sweating.
The alarmed moderator approaches and asks what's wrong.
"I finished the exam in half an hour," she replies. "Now I'm rechecking my answers."