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  • Math Experts Split the CheckAuthor(s): Ben OrlinSource: Math Horizons, Vol. 21, No. 3 (February 2014), pp. 18-19Published by: Mathematical Association of AmericaStable URL: .Accessed: 31/05/2014 22:36

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  • Math Experts Split theCheck

    Ben Orlin

    E ngineer: Remember to tip 18 percent, everybody.Mathematician: Is that 18 percent of the pretax total, or of the total with tax?Physicist: You know, its simpler if we assume the system doesnt have tax.Computer Scientist: But it does have tax.Phys: Sure, but the numbers work out more cleanly if we dont pay tax and tip. Its a pretty small error term. Eng: What you call a small error, I call a collapsed bridge.Economist: Dont get me started on taxes! If there were no taxes, I would have ordered a second soda. But instead, the government intervened, and by increasing transaction costs, prevented an exchange that would have benefited both the restaurant and me.Eng: You did order a second soda.Econ: In practice, yes. But my argument still holds in theory.

    The computer scientist lays a smart phone on the table.CS: OK, Ive coded a program to help us compute the check.Math: Hmmph. Any idiot could do that. Its a trivial problem.

    CS: Do you even know how to code?Math: Why bother? Learning to code is also a trivial problem.Eng: Uh . . . your program says we each owe $8,400.CS: Well, I

    havent debugged it yet, if thats what youre getting at.Phys: This is a waste of time. Lets just split it evenly.Econ: No! Thats so ineffcient. Lets each write down the amount were willing to put in, then auction off the remainder at some point on the contract curve.Phys: Huh?Math: Like most economics, thats just gibberish with the word auction in it.Eng: Look, its simple. Total your items, add 8 percent tax, and 18 percent tip.Math: Sure. Does anybody know 12 plus 7?CS: You dont?Math: What do I look like, a human calculator? Numbers are for children, half-wits, and bored cats.

    The engineer looks at the cash theyve gathered.Eng: Is everyones money in? It seems were a little short . . .Phys: How short?Eng: Well, the total was $104, not including tip . . . and so far weve got $31.07 and an old lottery ticket.Phys: Close enough, right? Its a small error term.Math: Which of you idiots wasted your money on a lot-tery ticket?Econ: I should mention that Im not planning to eat here again. Are any of you?CS: What does that matter?Econ: Well, in a noniterated prisoners dilemma, the dominant strategy is to defect.Eng: Meaning?Econ: We should be tipping 0 percent, since well never see that waiter again.Math: Thats awful.

    18 February 2014 : : Math Horizons : :

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  • Phys: Will the waiter really care0 percent, 20 percent? Lets not split hairs. Its a small error term.

    The engineer looks up from a graphing calculator.Eng: All right. Ive computed the precise amount each of us should pay, using double integrals and partial derivatives. I triple-checked my work.Math: Didnt we all order the same thing? You could have just divided the total by fi ve.Eng: I could? I mean . . . of course I could! Shut up! You think youre so clever!Econ: So, were all agreed on a 0 percent tip?CS: Well . . . the waiter did bring only two orders of fries for the table.Phys: We only ordered two.CS: Exactly. We got the 1st order, and the 2nd, but never the 0th.Econ: Ill be frank. At this point, my self-interest lies in not paying at all. And the economy prospers when we each pur-sue our individual self-interest. See you later!

    The economist dashes off . The engineer and computer scientist glance at one another, then follow.Math: Looks like its just you and me now.Phys: Good. The two-body problem will be easier to solve.Math: How?Phys: By reducing it to a one-body problem.

    The physicist scampers away.Math: Wait! Come back here!Waiter: I notice your friends have gone. Are you done with paying the check?Math: Well, Ive got a proof that we can pay. But I warn you: Its not constructive.

    Since completing his BA in math in 2009, Ben Orlin has taught high school courses including calculus, sta-tistics, psychology, biology, and (somewhat dubiously) earth science. He has written forSlateandThe Atlantic, and he blogs atMath with Bad Drawings (

    Zach Weinersmith,

    Ty Devries,

    Uncountable sets

    . . . Infi nity-one! Infi nity-two! Infi nity . . .

    Grant Snider, : : Math Horizons : : February 2014 19

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