A teacher wanted to teach a special lesson to his students, and for that he gave them the opportunity to choose between three exams: one of fifty questions, one of forty and one of thirty. Those who chose the thirty put a "C", no matter that they answered all the questions correctly.
Those who chose the forty put a "B", even if more than half was wrong. And those who chose the fifties put an "A", although they had been wrong in almost all.
As the students did not understand anything, the teacher explained: "Dear students, let me tell you that I was not examining your knowledge, but your willingness to point to the top".
