While seeing a 56 y/o male:
Me: How much do you smoke?
Patient: Not much, I'll only buy a pack on a day.
Me: A pack a day, that's a lot, that's 20 cigarettes a day. That means you're smoking almost 1 an hour.
Patient: No I don't.
Me: Aren't there 20 cigarettes in a pack?
Me: So you smoke 20 cigarettes a day?
Patient: No, when a buy a pack on a day it will usually last me 4-5 days before I have to buy another pack.
Me: Oh, I see. So you're smoking 4-5 cigarettes a day...hopefully you can continue to get even lower than that.
Actually, my initial thought was, "oops, my bad, ...sorry!"