Mathematician: Is that 18% of the pre-tax total, or of the total with tax?
Physicist: You know, it’s simpler if we assume the system doesn’t have tax.
Computer Scientist: But it does have tax.
Physicist: Sure, but the numbers work out more cleanly if we don’t pay tax and tip. It’s a pretty small error term. Let’s not complicate things unnecessarily.
Engineer: What you call a “small error,” I call a “collapsed bridge.”
Economist: Forget it. Taxes are inefficient, anyway. They create deadweight loss.
Mathematician: There you go again…
Economist: I mean it! 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 me and the restaurant.
Economist: In practice, yes. But my argument still holds in theory.
The computer scientist lays a smart phone on the table.
Computer Scientist: Okay, I’ve coded a program to help us compute the check.
Mathematician: Hmmph. Any idiot could do that. It’s a trivial problem.
Computer Scientist: Do you even know how to code?
Mathematician: Why bother? Learning to code is also a trivial problem.
Engineer: Uh… your program says we each owe $8400.
Computer Scientist: Well, I haven’t de-bugged it yet, if that’s what you’re getting at.
Economist: No! That’s so inefficient. Let’s each write down the amount we’re willing to put in, then auction off the remainder at some point on the contract curve.
Mathematician: Like most economics, that’s just gibberish with the word “auction” in it.
Engineer: Look, it’s simple. Total your items, add 8% tax, and 18% tip.
Mathematician: Sure. Does anybody know 12 plus 7?
Computer Scientist: You don’t?
Mathematician: What do I look like, a human calculator? Numbers are for children, half-wits, and bored cats.
The engineer looks at the cash they’ve gathered.
Engineer: Is everyone’s money in? It seems we’re a little short…
Physicist: How short?
Engineer: Well, the total was $104, not including tip… and so far we’ve got $31.07 and an old lottery ticket.
Physicist: Close enough, right? It’s a small error term.
Mathematician: Which of you idiots wasted your money on a lottery ticket?
Economist: I should mention that I’m not planning to eat here again. Are any of you?
Computer Scientist: What does that matter?
Economist: Well, in a non-iterated prisoner’s dilemma, the dominant strategy is to defect.
Economist: We should be tipping 0%, since we’ll never see that waiter again.
Computer Scientist: That’s awful.
Physicist: Will the waiter really care – 0%, 20%? Let’s not split hairs. It’s a small error term.
The engineer looks up from a graphing calculator.
Engineer: All right. I’ve computed the precise amount each of us should pay, using double integrals and partial derivatives. I triple-checked my work.
Mathematician: Didn’t we all order the same thing? You could have just divided the total by five.
Engineer: I could? I mean… of course I could! Shut up! You think you’re so clever!
Computer Scientist: Well… the waiter did only bring two orders of fries for the table.
Physicist: We only ordered two.
Computer Scientist: Exactly. We got the 1st order, and the 2nd, but never the 0th.
Economist: I’ll be frank. At this point, my self-interest lies in not paying. And the economy prospers when we each pursue our individual self-interest. See you later!
The economist dashes off. The engineer and computer scientist glance at one another, then follow.
Mathematician: Looks like it’s just me and you, now.
Physicist: Good. The two-body problem will be easier to solve.
Physicist: By reducing it to a one-body problem.
The physicist scampers away.
Mathematician: Wait! Come back here!
Waiter: I notice your friends have gone. Are you done with paying the check?
Mathematician: Well, I’ve got a proof that we can pay. But I warn you: it’s not constructive.
Thanks for reading! (And for your benign tolerance of my whiteboard doodles.) You might also enjoy “A Math Professor Consults on a Hollywood Movie.”