A professor of mathematics sent a fax to his wife.

Dear Wife,

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

Your Husband ……………..

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

Dear Husband,

You too are 54 years old, and by the time you
receive this letter, I will be at the Breakwater
Hotel with the 18-year-old pool boy. Since you are
the mathematician, you will appreciate the fact that
18 goes into 54 more times than 54 goes into 18.
Therefore, don't wait up.