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Dr. Shapiro's Puzzle of the Day

Today's Puzzle

Friday, September 25
Can you name the two cookie brands shown at left? They are produced in New England and Germany, respectively, and both were invented in 1891, but no one is sure which came first.

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Yesterday's Puzzle + Solution

"Kidney bean–shaped", "cardioid", "colored according to", "sea horse valley", and "assumed to have escaped" are phrases from the MathWorld encyclopedia article on what subject?

Hint Here are a few more phrases from that page: "computer-generated", "defined by iterating", and "increasingly convoluted". No mention is made of biscotti.

Solution It's the Mandelbrot set. (And in case you wondered about the biscotti reference: mandelbrot.)

When Benoît Mandelbrot sent the first low-resolution images of his fractal directly to a (primitive) printer, he noticed the roughness of the boundary but assumed he was just seeing dirt from the print head. Only when those splotches showed up in the same place on repeated printouts did he realize he had something worthy of deeper investigation. History does not record whether he said to himself, "Weird flecks, but OK!"

Congratulations to yesterday's solvers Jessica, Inca, Maddy, Leo S., Jacob C., Mr. Gregg, and Jason. 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.