AHA! Puzzle This
By Michael H. Pryor
MAKE’s favorite puzzles. (When you’re ready to check your answers, visit
makezine.com/16/aha.)
Illustration by Roy Doty
World Series Survival left over, he will accuse you of stealing and kill you.
The CIA asks you to infiltrate the North Korean You have no money, except for the money he’s given
leadership. After attempting to enter the country, you, and maybe a couple hundreds in your pocket
you’re captured by Kim Jong-il. But it turns out he’s (for rounding errors).
a fan of American baseball, and as the World Series There are bookies you can place bets with in
is about to start, he chooses to give you a sporting Pyongyang, but unfortunately they will only accept
chance to be freed. bets for one game at a time, not for the whole
The Yankees are playing the Red Sox and the series. Since each game is a coin flip and the out-
2 teams are perfectly, absolutely matched. Each come of previous games doesn’t change that fact,
game is a coin flip — the chances of a win for both you can place whatever size bet you want on each
are exactly 50%. The outcome of any previous game, at fair odds ($1 wagered wins $2 back), right
games does not give you any information about before they occur (after any previous games have
who’ll win the next game. been played). Obviously you must have the money
The Dear Leader wants to bet a million bucks that in your pocket to place the bet.
the Yankees will win the entire series. He will front Remember, the World Series is a 7-game series
you the cash (i.e., he’ll give you $1 million up front, where the first team to win 4 individual games is
and you give him $2 million back if the Yankees win, declared the winner.
and give him nothing if the Yankees lose). How should you place your bets to guarantee
If you decline the bet, he will kill you. If the Yankees you’ll have 2 million bucks for Kim Jong-il if the
win and you don’t have all $2 million to pay him, he Yankees win the entire series, and $0 if they lose?
will kill you. If the Yankees lose, and you have money
Michael Pryor is the co-founder and president of Fog Creek Software. He runs a technical interview site at
techinterview.org.
Make: 193
