Gamblers Take Note: The Odds in a Coin Flip Aren’t Quite 50/50
Gamblers Take Note: The Odds in a Coin Flip Aren’t Quite 50/50
Imagine you’re at a bar and another patron offers you the following wager. He’s going to flip a coin — a standard U.S. penny like the ones seen above — a dozen or so times. If it comes up heads more often than tails, he’ll pay you $20. If it comes up tails more than heads, you pay him the same. There are no hidden tricks. It’s a fair bet — safe to take, if you’re looking for a 50/50 chance.
Now, imagine the same offer, except that instead of flipping the coin, the other patron tells you he’s going to spin it. In fact, he’ll even let you provide the penny, just to guarantee there is no funny business. Twenty-five spins and if it comes up heads more often than tails, he’ll give you $20 again. But if tails comes up more often, you owe him $20.
Fair bet? Not if Persi Diaconis is right.