Professor of Mathematics

A professor of mathematics sent a letter to his wife. It read:

"Dear wife,

You must realise that you are 54 years old and I have certain needs which you are no longer able to satisfy. I am otherwise happy with you as a wife and I sincerely hope you will not be hurt or offended to learn that by the time you receive this letter, I will be at Radisson Blu Hotel with my 18 years old student. I'll be home before midnight.

Your Husband".

When he arrived at the hotel, there was a letter waiting for him that read as follows:

"Dear Husband,

You too are 54 years old and by the time you receive this, I will be at Nicon Hotel with the 18-year-old houseboy. Being the brilliant mathematician that you are, you can easily appreciate the fact that 18 goes into 54 a lot more times than 54 goes into 18."