A woman comes home and find a letter from her husband on the dinner table. She opens it and reads:
"My Dear Wife,
You will surely understand that I have certain needs that you, as a 54 year-old, can no longer satisfy. I'm very happy with you and I value you as a good wife. However, after reading this letter, I hope you will not wrongly interpret the fact that I will be spending the evening with my 18 year-old secretary at the Comfort Inn. Please don't be upset, I shall be back before midnight."
When the man came home late that night, he found a reply to his letter on the dining room table:
"My Dear Husband,
I received your letter and thank you for your honesty about my being 54 years old. I would like to take this opportunity to remind you that you are also 54 years old.
I would like to inform you that, while you read this, I will be at the Hotel Fiesta with Michael, one of my students, who is also an assistant tennis coach. He is young, virile and, like your secretary, he is 18.
You, being a successful businessman with an excellent knowledge of maths, will understand that we are in the same situation, although with one small difference - 18 goes into 54 a lot more times than 54 goes into 18...