While taking a math test in class, Bart reads a word problem and daydreams about it.
Bart [interior monologue]: At 7:30am, an express train traveling 60 miles per hour leaves Santa Fe bound for Phoenix, 520 miles away. At the same time, a local train traveling 30 miles an hour carrying 40 passengers leaves Phoenix bound for Santa Fe. It’s eight cars long and always carries the same number of passengers in each car. An hour later, the number of passengers equal to half the number of minutes past the hour get off, but three times as many plus six get on. At the second stop, half the passengers plus two get off but twice as many get on as got on at the first stop.
Train conductor: Ticket, please.
Bart: I don't have a ticket!
Train conductor: Come with me, boy.
[He drags Bart off. Numbers circle Bart's head.]
We've got a stowaway, sir.
Bart: I'll pay! How much?
[The train engineer is Martin, shoveling numbers into the engine.]
Martin: Twice the fare from Tucson to Flagstaff minus two-thirds of the fare from Albuquerque to El Paso! Ha ha ha ha!
2. Bart eats lunch with his new classmates at the school for gifted students.
Child genius: Tell you what, Bart, I’ll trade you the weight of a bowling ball on the eighth moon of Jupiter from my lunch, for the weight of a feather on the second moon of Neptune from your lunch.
Bart (unsure): Well, OK.
Child genius (laughs): There you go!
[He takes Bart’s sandwich and gives him a grape.]
3. Bart’s new teacher writes at the board.
Teacher: So y equals r-cubed over three, and if you determine the rate of change in this curve correctly, I think you will be pleasantly surprised.
[The students laugh except for Bart who appears confused.]
Teacher: Don’t you get it, Bart? Derivative dy equals three r-squared dr over three, or r-squared dr, or r dr r. Har-de-har-har! Get it?
See the r dr r classroom worksheet.