Do you ride public transportation? Then you've got a head start on this week's Sunday Puzzle.

Sunday Puzzle #24: Timing Trains

A young man lives in Manhattan near a subway express station. He has two girlfriends, one in Brooklyn, one in the Bronx. To visit the girl in Brooklyn, he takes a train on the downtown side of the platform; to visit the girl in the Bronx, he takes a train on the uptown side of the same platform. Since he likes both girls equally well, he simply takes the first train that comes along. In this way, he lets chance determine whether he rides to the Bronx or to Brooklyn. The young man reaches the subway platform at a random moment each Saturday afternoon. Brooklyn and Bronx trains arrive at the station equally often—every 10 minutes. Yet for some obscure reason he finds himself spending most of his time with the girl in Brooklyn: in fact, on the average, he goes there 9 times out of 10. Can you think of a good reason why the odds so heavily favor Brooklyn?

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We'll be back next week with the solution – and a new puzzle! Got a great brainteaser, original or otherwise, that you'd like to see featured? E-mail me with your recommendations. As always, be sure to include "Sunday Puzzle" in the subject line!

Art by Tara Jacoby


SOLUTION To Sunday Puzzle #23: Statements of Truth

Last week, I presented you with ten self-referential statements. Your task was to figure out which of the statements were true.

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A number of you solved this puzzle quite quickly. I believe the first to do so was commenter OncomingStorm_in_a_Browncoat_with_a_stake, who correctly identified statement #9 as the one and only true statement. In this list, every individual statement contradicts every other statement, so it is impossible for more than one statement to be true. In a list of ten statements, this means "nine of the statements are false," as the ninth statement maintains.

If you're still confused, commenter Remy Porter supplied a tidy inductive argument for why, in a list of N statements of the form "Exactly _ of this/these statements is/are false," statement N-1 will always be the one true statement.

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Previous Weeks' Puzzles

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