How old are you?

Nurse: How old are you? Patient: None of your business. Nurse: But the doctor must know your age for his records. Patient: Well, first, multiply twenty by two, then add ten. Got that? Nurse: Yes. Fifty. Patient: All right, now subtract fifty, and tell me, what do you get? Nurse: Zero. Patient: Right. And that's exactly the chance of me telling you my age.
Originally published November 14, 2002.