There's the "I have a system to win at craps! I'll teach you the system, you play under my guidance, and you just have to pay 25% of your winnings! And if you lose, you pay me *nothing*!" I think that this one, along with a couple of related ones (possibly done with horse racing instead of craps) are in one of Feynman's books. More generally, you can think of casino gambling as such a scam. I think that most people who play blackjack in a casino cannot answer the following question: "So you get to split and to double down, and the dealer doesn't; you get paid 3-2 on blackjack, and the dealer doesn't. You can use whatever strategy you like, after seeing one of the dealer's cards, and the dealer has to use a simple fixed strategy. Why does the dealer have an advantage?" Where are you teaching this class?

-----Original Message----- From: math-fun-bounces+andy.latto=pobox.com@mailman.xmission.com [mailto:math-fun-bounces+andy.latto=pobox.com@mailman.xmission.com]On Behalf Of James Propp Sent: Thursday, January 19, 2006 11:34 PM To: math-fun@mailman.xmission.com Subject: [math-fun] mathematical cons

I'm teaching a course on quantitative reasoning for an audience of nearly two hundred math-averse students, and one of the ways I'm hoping to "sell the product" to them is to pitch the course as a kind of self-defense art that helps you not get ripped off by used car dealers, cell-phone companies, credit-card companies, banks, etc.

For instance, I'll talk about the scam wherein the scammer sends free investment advice to 1024 people (half of whom get one piece of advice and half of whom get a conflicting piece of advice), then sends free advice to the 512 who got good advice on the first round (again splitting his advice half-and-half), then sends free advice to 256 people, and so on, and finally starts to ask a small number of people to pay a lot of money, hoping that they'll reason that someone who's been right so often must be onto something.

I'll also show the class the grifting scene in "Paper Moon".

Can any of you think of other good mathematical cons, or good resources for finding out about them?

("Ricky Jay's Big Book of Math Hustles" would be perfect if such a book existed!)

Jim

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