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Dr. Shapiro's Puzzle of the Day

Today's Puzzle

Thursday, October 8
Today I'm featuring a guest puzzle written by S. Neilson for LearnedLeague, an online trivia game. I liked this question so much I had to share it with you.

Which country is crossed by the train shown at left?

(Don't give up if you don't recognize it. You can puzzle it out!)

   


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Yesterday's Puzzle + Solution

My father and I have the same birthday!

Wait, no we don't. Our birthdays are actually 144 (sometimes 145) days apart. But if you read our birthdays as fractions (month/day), then his birthday is the reduced form of mine. What are our birthdays?

BONUS PUZZLE (I thought this would be too obscure for a regular PotD... prove me wrong!):
In the original illustrations for Alice in Wonderland, a certain "fraction" appears on the Mad Hatter's hat. (It's not really a fraction—it's a price tag in shillings and pence.) If you reduce that "fraction", you get the logo of what Cincinnati-based institution with over 1100 branches?

Solution Our birthdays are January 6 and May 30.

A good place to start is the "sometimes 145" clue. Why aren't our birthdays always the same number of days apart? One must be before February 29 and the other must be after.

144 days is slightly less than 5 months. The birthday with the smaller month must also have the smaller date (because of how fractions reduce), so we're either looking at early January and late May, or early February and late June. Then the only pair of dates that are far enough apart in their respective months is 1/6 and 5/30. (Potentially, the "144 or 145 days" between our birthdays might have wrapped around past New Year's—I leave it to you to check that this does not create any additional solutions!)

As for the bonus puzzle... the Mad Hatter sports a 10/6, which reduces to 5/3, the logo of Fifth Third Bank.

Congratulations to yesterday's solvers Maddy, Yana, Nico, Cloe, Jessica, Leo S., Jacob C., and Zachary S. The last three also solved the bonus puzzle with a little help from Google. Thanks to everybody who made a guess!

About This Site

Though he now teaches mathematics, Dr. (né Mr.) Shapiro's first job in a K–12 school was as a lunch monitor in Davis, CA. It was there that he originated the Puzzle of the Day, even rewarding correct answers with tickets in denominations like "15 points" (though without a clear idea of how he'd ultimately redeem these). Dr. Shapiro's favorite puzzle from this pre-professional era was "Tell me the location of the beehive on this campus."

Ten years later, Dr. Shapiro revived Puzzle of the Day at Proof School, writing each day's puzzle on a name tag. After 600 puzzles or so, he was just starting to feel normal about students reading his chest all the time when campus closed and the puzzle, like the rest of our lives, moved online. New puzzles are posted daily on school days.

Want to catch up on old PotDs? There's an archive currently containing puzzles from March to June 2020.