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*!"
That's a new one on me. I like it!
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.
Can anyone provide the reference?
Where are you teaching this class?
The University of Wisconsin. There are casinos nearby, and if the class were smaller, I might propose a field trip. But with nearly 200 students, I don't think that's going to work. Incidentally, I just rented "Paper Moon", and I watched the grifting scene closely (about 24 minutes into the film), but the editing obscures what's going on with the grift. Here's what happens, as far as I can tell: **************************************************************** SALESLADY Ain't she got a sweet little face... somehow. MOSES Well, seeing how I just got paid today, we'll take a ribbon in each color. How much that going to set me back? SALESLADY Well, that'll be 15 cents. Bought my grandchildren ribbons just like this last holiday time. MOSES Grandchildren? I don't believe it. - You break a 5? (He hands her a $5 bill; she takes it.) SALESLADY Well, you can believe it, all right. I'm just as old as I look. - Well, now, here you be... That's one, two, three, four, five. (She gives him 85 cents in change and four $1 bills.) MOSES You know, this old wallet of mine is about to bust its sides. I'll give you five ones 1's, you give me that $5 bill. - How many grandchildren you got all together? (He gives her five $1 bills, and takes from her the $5 bill.) SALESLADY Well, I got two little granddaughters... a nine year old, a ten year old... two grandsons near 16 and I got a grandson 35 years old. MOSES Come on, you're pulling my leg. - Why don't you just give me a $10 bill? Here's the 5 and five 1's, there. (He gives her the $5 bill.) That way I won't be so quick to see it break apart. (She gives him a $10 bill.) Six children, huh? My, my, my... SALESLADY I've got a daughter, 51. MOSES Oh, now, I don't mean to be handing you no line, but that's just pretty hard to believe you got a 51-year-old child. SALESLADY You can believe it, all right. MOSES Well, I'm afraid I'd have to see it to believe it. - Much obliged. See you again. SALESLADY Y'all come back! (Moses and Addie Pray leave, quickly.) That just don't seem quite right... somehow. **************************************************************** We don't actually see Moses get the $5 bill from her after he's given her some singles (the camera cuts to Addie, so we don't see what's going on at the cash register), but I'm figuring that he must have gotten the $5 from her while the camera's pointing at Addie, because (a) if he hadn't, then he wouldn't make any profit on the transaction, and (b) he goes on to say "Here's the 5 and five 1's, there," where and the use of the word "the" suggests that it's a $5 bill they've seen before, namely, the one he gave her at the beginning. Have I parsed the scam correctly? (It's also possible that when he claims to be giving her five $1 bills, he's actually giving her just the four she gave him; it's hard for me to tell.) Jim