H E L L O
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Dr. Shapiro's Puzzle of the Day

Today's Puzzle

Thursday, February 11
I see this picture ALL THE TIME on my computer. It's never what I was looking for. Why does this happen?
(That's it. That's the puzzle.)

   


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Yesterday's Puzzle + Solution

When I saw this license plate, I thought "Cool, they've been doing this for over twenty years!"

But then I realized that an assumption I'd made was definitely wrong.

What was my original assumption and how did I realize it was wrong?

Solution License plates have to display a current registration sticker, like the blue "19" sticker in the upper right corner of the picture which indicates expiration in 2019. (I took this photo a while ago.)

The stickers cycle through five colors on a 5-year cycle. The strips decorating this plate are the stubs, which you'd normally throw away. (If you look closely, they say PEEL HERE.) I assumed that each year, when the car owner got their registration, they added another stub.

This theory started to fall apart when I noticed the suspiciously high ratio of orange/blue stubs to yellow/red. But the final blow came from the format of the license plate number. California plates used to have just three letters and three digits. When the possible plates were exhausted, the state switched to three digits and three letters. When those ran out, they added an extra digit at the beginning: first 1, then 2, etc. The extra digit didn't reach 7 until about 2013, so this plate is definitely not old enough to have accumulated 21 sticker stubs at a rate of one per year.

Maybe the driver works for the DMV. ¯\_(ツ)_/¯

Congratulations to yesterday's solvers; at least one part was solved by Jessica, Jacob C., Charlie, Leo S., Kate, Jason, and Mr. Gregg. 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 December 2020.