Man sends wife a fax

My Dear Wife,

You will surely understand that I have certain needs that you with your 54 years can no longer supply.
I am very happy with you and I value you as a good wife.
Therefore after reading this fax, 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 Hotel. Please don't be perturbed. I shall be back home before midnight.

When the man came home, he found the following letter on the dining room table...

My Dear Husband,

I received your fax and thank you for your honesty. I would like to take this opportunity to remind you that you are also 54 years old.
At the same time I would like to inform you that while you read this, I will be at the Hotel Fiesta with Michael my tennis coach, who, like your secretary, is also 18 years old.

As a successful businessman with your excellent knowledge of math, you 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.

Therefore, I will not be back before lunchtime tomorrow