You and I each have 14 dollars. I flip a fair coin repeatedly; if it comes up heads I pay you a dollar, but if it lands tails you pay me a dollar. On average, how many times will I flip the coin before one of us runs out of money?
I know that the chance of each of us winning is equal (1/2), but I have no idea what the average number of flips should be. I think it's 28 but it's just a guess.