Final Exam

The blonde reported for her university final examination that consists of yes/no type questions.  She takes her seat in the examination hall, stares at the question paper for five minutes and then, in a fit of inspiration, takes out her purse, removes a coin and starts tossing the coin, marking the answer sheet:  Yes, for Heads, and No, for Tails.  Within half an hour she is all done, whereas the rest of the class is still sweating it out.  During the last few minutes she is seen desperately throwing the coin, muttering and sweating.  The moderator, alarmed, approaches her and asks what is going on.  "I finished the exam in half an hour, but now I'm rechecking my answers."