Walt sent me this puzzle (reworded from this set of great puzzles from Communications of the ACM; you can get it by accessing from a University or library).
Alice and Bob roll 2 standard 6-sided dice, note their sum, and repeat.
Alice wins if a 7 is rolled, and then followed immediately by another 7.
Bob wins if an 8 is followed immediately by a 7. They continue rolling until somebody wins. Who has the better odds of winning?
Of course the answer is the non-intuitive one. Can you figure out why? As a person with a long-time fondness for craps (I know lots of people who are no good at probability, except when it involves two dice), this seems to me like the ultimate sucker bet to offer someone.
This post was developed on WorkingWiki at Sucker bet. Click to see more discussion (and a link to the answer.)