I just bought three dozen doughuts for Blue Shirt Tuesday at work and the checkout clerk, who was obviously brand new, as in I was his second customer ever, tried to charge me for 36 doughnuts rather than 3 dozen and they go for about $6 the dozen, but the charge was $24.
So I pointed this out, a manager ended up coming, and we got it sorted out in short order. I tried to make a joke, saying, "If I do that about a million more times, then all the math classes I've taken will have been worth it" [paraphrase].
Silly me, rather than a million, obviously, the answer would've probably been more like two thousand...out-of-pocket, anyway.
Innumeracy versus skill in arithmetic -- not always the same thing.