Set high goals

A teacher wanted to teach them a very special lesson to their students, for it gave them the great opportunity to choose between three exams:
-the first of fifty questions.
-the second of forty.
-the third of thirty.
The students who chose the thirty exam put a "C" on them, regardless of whether they had correctly answered all the questions; Those who chose the one in the 40 gave them a "B", even though half of the answers were wrong; And those who chose the fifty gave them an "A", even if they had been wrong in most questions.

The students did not understand anything about what happened with their exams, the teacher explained: Dear students: let me tell you that I was not qualifying their knowledge, but their great desire to aim high, set high goals.