Student: I want to ask you something. If you give the right answer, I take my bad mark and I go. But if you do not know the answer, you will give me a good mark.
Professor: Okay, okay. Ask it.
Student: What is legal but not rational? What is rational but illegal? And what is neither rational nor illegal?
After the professor thinks well, he can not give an answer. And he gives good mark to his student. Then the professor calls for the best student and asks the same questions.
The student answers immediately:
You are 63 years old and you are married to a 35-year-old young lady. It is legal but not rational. Your wife has a lover 25 years old. It is rational but illegal.
You gave good mark to a student and he passed the exam who is your wife’s lover.
It is neither rational nor legal.