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Try Solving This Riddle From a High School Math Competition

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Math olympiads feature some of the brightest minds to enter high school. The problems given to competitors are meant to be tricky, but there’s one question that’s so notorious it even has its own Wikipedia page.

The "Cheryl’s Birthday" riddle first appeared on a math olympiad test given to students in Singapore. Local television presenter Kenneth Kong posted a picture of the original text on Facebook in 2015. The clunky English makes for a riddle that's hard to decipher, so The New York Times published an edited version that reads as follows:

"Albert and Bernard just met Cheryl. 'When’s your birthday?' Albert asked Cheryl. Cheryl thought a second and said, 'I’m not going to tell you, but I’ll give you some clues.' She wrote down a list of 10 dates: May 15, May 16, May 19, June 17, June 18, July 14, July 16, August 14, August 15, August 17. 'My birthday is one of these,' she said. Then Cheryl whispered in Albert’s ear the month—and only the month—of her birthday. To Bernard, she whispered the day, and only the day. 'Can you figure it out now?' she asked Albert. Albert: I don’t know when your birthday is, but I know Bernard doesn’t know, either. Bernard: I didn’t know originally, but now I do. Albert: Well, now I know, too! When is Cheryl’s birthday?"

If you read through this quickly, it’s easy to get lost. How is it possible to guess someone’s birthday when you only have one half of the date? And how could Albert and Bernard help each other guess correctly without sharing their intel out loud? The secret lies in the possible dates Cheryl chooses to share.

In her list, every day is repeated once except for the 18th and the 19th—so if she had whispered “18” in Bernard’s ear he would immediately know her birthday was June 18, and if she’d whispered “19” he’d know it was May 19. Bernard confirms it couldn’t be either of those dates when he says he “didn’t know originally.” That means June and May are no longer options for Albert, which narrows it down to five possibilities: July 14, July 16, August 14, August 15, and August 17.

When Bernard says “I didn’t know[…]but now I do” that disqualifies 14, because in that case he would have two potential answers (July 14 and August 14) to choose from. These leaves three dates—July 16, August 15, and August 17—that could be correct. When Albert says, “Well, now I know too!” he eliminates July from the equation because that’s also a case where he’d be left with two options. July 16 is therefore the one true answer.

Does your head hurt yet? Unfortunately, math problems intended for grade-schoolers in Singapore don’t get much simpler. Check out this perplexing homework problem given to first-graders if you need convincing.

[h/t The New York Times]

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National Geographic Ranks The 25 Happiest Cities in the Country
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Feeling unhappy? Maybe it's time to move. National Geographic recently released rankings of the 25 happiest cities in the U.S. The results: Eight of the 25 locations are in the Golden State, but the honor of No. 1 happiest city goes to Boulder, Colorado.

The rankings are based on 250,000 interviews conducted in 190 metropolitan areas between 2014 and 2015. The survey—developed by Dan Buettner, author of the new book The Blue Zones of Happiness, and Dan Witters, a senior scientist at Gallup—looked for data points that are correlated with life satisfaction and happiness, like whether or not you exercise, if you feel safe in your community, whether you feel like you live within your means, and whether you feel like you are reaching your goals.

A map of the U.S. showing which cities made the top 25 happiest cities index.
Courtesy National Geographic

Of course, all that isn’t necessarily the result of your geographical location. But you don’t see cities like Los Angeles or New York—where wealth is also clustered—on the list, so presumably San Franciscans are doing something a little differently.

Take a look for yourself. Here are the 25 happiest places in the U.S., according to the results.

1. Boulder, Colorado
2. Santa Cruz-Watsonville, California
3. Charlottesville, Virginia
4. Fort Collins, Colorado
5. San Luis Obispo-Paso Robles-Arroyo Grande, California
6. San Jose-Sunnyvale-Santa Clara, California
7. Provo-Orem, Utah
8. Bridgeport-Stamford, Connecticut
9. Barnstable Town, Massachusetts
10. Anchorage, Alaska
11. Naples-Immokalee-Marco Island, Florida
12. Santa Maria-Santa Barbara, California
13. Salinas, California
14. North Port-Sarasota-Bradenton, Florida
15. Urban Honolulu, Hawaii
16. Ann Arbor, Michigan
17. San Francisco-Oakland-Hayward, California
18. Colorado Springs, Colorado
19. Manchester-Nashua, New Hampshire
20. Oxnard-Thousand Oaks-Ventura, California
21. Washington, D.C.-Arlington-Alexandria, Virginia/Maryland/West Virginia
22. Minneapolis-St. Paul-Bloomington, Minnesota/Wisconsin
23. San Diego-Carlsbad, California
24. Portland-South Portland, Maine
25. Austin-Round Rock, Texas

You can grab a copy of November’s National Geographic to read more about the world’s happiest places.

The cover of Dan Buettner’s The Blue Zones of Happiness and the cover of November 2017’s National Geographic.
National Geographic
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Here's How to Turn an IKEA Box Into a Spaceship
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Since IKEA boxes are designed to contain entire furniture items, they could probably fit a small child once they’re emptied of any flat-packed component pieces. This means they have great potential as makeshift forts—or even as play spaceships, according to one of the Swedish furniture brand’s print ads, which was spotted by Design Taxi.

First highlighted by Ads of the World, the advertisement—which was created by Miami Ad School, New York—shows that IKEA is helping customers transform used boxes into build-it-yourself “SPÄCE SHIPS” for children. The company provides play kits, which come with both an instruction manual and cardboard "tools" for tiny builders to wield during the construction process.

As for the furniture boxes themselves, they're emblazoned with the words “You see a box, they see a spaceship." As if you won't be climbing into the completed product along with the kids …

Check out the ad below:

[h/t Design Taxi]

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