Barbara reported for her final exam, knowing she was academically challenged, to say the least.

But she was confident, because her exam consisted only of yes or no questions. And this time, 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 had answered every question.

But then as time ticked on, there was a problem. She desperately tossed the coin, again and again muttering under her breath and sweating.

The moderator asked what was going on.

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