Barbara reported for her university final examination early, knowing she was academically challenged, to say the least. But she was confident, because her exam consisted only of yes or no questions. And she had a plan!

She took her seat in the examination hall, produced a coin, and started flipping the coin for each answer. Basking in her genius, she marked the answer sheet yes for heads and no for tails.

Within half an hour she was done. But as she put the rest of her time to use, she had a problem.

As time ticked away, she desperately tossed the coin, muttering under her breath and sweating. The moderator, alarmed, approached her and asked what was going on.

Barbara said, "I finished the exam early, but I'm re-checking my answers and nothing matches up."