Nurse to Patient: How old are you, Mrs.Smith?
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?
Patient: And that’s exactly the chance of me telling you my age.