A professor of mathematics sent a fax to his wife. It read: Dear wife, You must realize 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 having a great time at the Grand Hotel with my 18 year old teaching assistant. I'll be home before midnight. Sincerely, your Husband.

The wife responded:

Dear Husband, Your letter made me realize that you too are 54 years old, and by the time you receive this, I will be at the Breakwater Hotel with the 18 year old pool boy. Being the brilliant mathematician that you are, you can easily appreciate the fact that I am going to be having a far better time than you are because: 18 goes into 54 a lot more times than 54 goes into 18. Don't wait up