This post at Not Always Right reminded me of something from when I worked at a pizza place many years ago.
Someone called to order a pizza, and I answered the phone. It went something roughly like this:
Him: "How big is your medium pizza?"
Me: "The medium is 12 inches across."
Him: "And how big is the large?"
Me: "The large is 15 inches across."
Him: "So how much more pizza is that?"
Me (thinking): Is this guy serious?
Me (aloud): "One moment, sir."
I grabbed the calculator and once again cursed it for not being a "real" calculator--"real" to me meaning a scientific calculator with parenthesis function--and after several seconds spoke again.
Me: "About 63 square inches."
Him (laughing): "And how do you figure that?"
Me: "The area of a circle is pi times the radius squared, so 3.141592654 times 7.5 squared minus pi times 6 squared gives me the difference between the two pizzas."
Him: "Okay...but it's 3 inches bigger, right?"
Me: (pause) "...Right." While thinking: He needed me to confirm that the difference between 12 and 15 is 3?
Him: "I better take the large, then."