A professor of mathematics sent a text message to his wife:
You must realize that as you are 54 years old, I have certain needs which you are no longer able to satisfy. I am otherwise happy with you as a wife. I sincerely hope 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 will be home before midnight.
When the professor arrived at the hotel, an email waited for him:
You, too, are 54 years old, and by the time you receive this message, I will be at the Breakwater Hotel with the 18 year old pool boy. Since you are a mathematician, you will appreciate that 18 goes into 54 more times than 54 goes into 18. Therefore, don’t wait up.