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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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ESA/ATG
The European Space Agency Needs Help Naming Its New Mars Rover
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ESA/ATG

The European Space Agency is hosting a competition to find a snazzy new name for its ExoMars rover, Sky News reports. The rover will be deployed to Mars in 2020, so the winner would be playing a small role in the progress of space exploration.

At the contest's launch, British astronaut Tim Peake described Mars as a place where humans and robots will someday work together to search for evidence of life in our solar system. To this end, the ExoMars rover, which will land on Mars in 2021, will drill up to two meters into the planet’s soil and collect samples, the ESA notes. "The ExoMars rover is a vital part of this journey of exploration, and we're asking you to become part of this exciting mission and name the rover that will scout the Martian surface,” Peake said.

However, the agency is well aware of past public naming contests that have gone horribly wrong (we’re looking at you, Boaty McBoatface), so it’s rigged the rules to prevent such a spectacle. Instead of a public poll, suggestions will be submitted privately to the agency, which has created a panel of judges to choose the winning name.

The winner of the contest will also receive a trip to Stevenage, England, where they’ll get to see the Airbus facility where the rover is being pieced together. The contest is only open to citizens of the two dozen European countries that are partners in the ESA.

To enter, submit your name suggestion online before October 10, 2018, along with a brief explanation (under 150 words) of why your name should be chosen. Click the following PDF link to see the full terms and conditions [PDF].

[h/t Sky News]

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Fearless Man Slices 26 Watermelons on His Stomach in 60 Seconds, Setting New Record
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Ashrita Furman, a 63-year-old New Yorker who holds the world record for setting the most Guinness World Records, just achieved another one. This time, it was for the most watermelons sliced on top of his stomach in 60 seconds, Nerdist reports.

Furman came up with the idea for the record himself, and while he didn’t have any competition, Guinness stipulated that he had to slice at least 20 watermelons to be recognized. He managed to cut through 26 melons with his tool of choice, a katana, in less than a minute. (He walked away without a scratch.)

Check out this spectacle (and serious ab workout) for yourself:

“I’m really thrilled,” Furman told Reuters after pulling off the feat. “My first reaction is I’m relieved that I didn’t kill myself and the second is that I’m exhilarated because it is not only a skillful record, but also it’s something that I invented and now it’s out there and other people can challenge it.”

Furman, who has been called “Mr. Versatility,” currently holds more than 200 Guinness records. He set his very first record in 1979 after completing 27,000 jumping jacks, and he hasn’t slowed down since. In the past near-40 years he has set the record for—among other feats—the most knives caught in a minute (54); the greatest distance traveled while juggling on a pogo stick (4 miles, 30 feet); and most grapes caught in his mouth in one minute (86).

[h/t Nerdist]

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