Wife and Mistress

A doctor, a lawyer and a mathematician were discussing the relative merits of having a wife or a mistress.

The lawyer says:

- For sure a mistress is better. If you have a wife and want a divorce, it causes all sorts of legal problems.

The doctor says:

- It's better to have a wife because the sense of security lowers your stress and is good for your health.

The mathematician says:

- You're both wrong. It's best to have both so that when the wife thinks you're with the mistress and the mistress thinks you're with your wife, you can do some mathematics.