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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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Pig Island: Sun, Sand, and Swine Await You in the Bahamas
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When most people visit the Bahamas, they’re thinking about a vacation filled with sun, sand, and swimming—not swine. But you can get all four of those things if you visit Big Major Cay.

Big Major Cay, also now known as “Pig Island” for obvious reasons, is part of the Exuma Cays in the Bahamas. Exuma includes private islands owned by Johnny Depp, Tyler Perry, Faith Hill and Tim McGraw, and David Copperfield. Despite all of the local star power, the real attraction seems to be the family of feral pigs that has established Big Major Cay as their own. It’s hard to say how many are there—some reports say it’s a family of eight, while others say the numbers are up to 40. However big the band of roaming pigs is, none of them are shy: Their chief means of survival seems to be to swim right up to boats and beg for food, which the charmed tourists are happy to provide (although there are guidelines about the best way of feeding the pigs).

No one knows exactly how the pigs got there, but there are plenty of theories. Among them: 1) A nearby resort purposely released them more than a decade ago, hoping to attract tourists. 2) Sailors dropped them off on the island, intending to dine on pork once they were able to dock for a longer of period of time. For one reason or another, the sailors never returned. 3) They’re descendants of domesticated pigs from a nearby island. When residents complained about the original domesticated pigs, their owners solved the problem by dropping them off at Big Major Cay, which was uninhabited. 4) The pigs survived a shipwreck. The ship’s passengers did not.

The purposeful tourist trap theory is probably the least likely—VICE reports that the James Bond movie Thunderball was shot on a neighboring island in the 1960s, and the swimming swine were there then.

Though multiple articles reference how “adorable” the pigs are, don’t be fooled. One captain warns, “They’ll eat anything and everything—including fingers.”

Here they are in action in a video from National Geographic:

Photo Illustration by Lucy Quintanilla. Balloon/Poe, iStock
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History
When Edgar Allan Poe Pranked New York City—And Inspired Jules Verne
Photo Illustration by Lucy Quintanilla. Balloon/Poe, iStock

On April 13, 1844, a special extra of the New York Sun announced: “ASTOUNDING NEWS! … THE ATLANTIC CROSSED IN THREE DAYS! SIGNAL TRIUMPH OF MR. MONCK MASON’S FLYING MACHINE!!!” According to the article, a balloon heading from England toward Paris had been blown off-course and landed safely near Charleston, South Carolina. The “report” was submitted by a journalist who was also a well-known short-story writer: Edgar Allan Poe.

There was just one problem. He had made the whole thing up.

“The Balloon Hoax,” as it later became known, was Poe’s idea of a calling card. He had just moved to Manhattan, looking for work as a journalist. What better way to announce you’ve arrived than to prank an entire city?

The possibility of balloon travel had ignited the popular imagination since the 1780s, when the Montgolfier brothers built the first balloon to carry a man into the air. By the 1830s, balloonists had successfully crossed the British Channel, and they had begun talking about attempts to cross the Atlantic in earnest.

Newspapers were often full of the exploits of daring aeronauts, and the interest in ballooning apparently led to some fictional takes on the pursuit. Poe’s story in The Sun wasn’t the first: In 1835, Richard Adams Locke published a widely credited account of a balloon reaching the moon. The success infuriated Poe, who had just two months earlier published a story about a man returning from the moon in a balloon, “Hans Pfaall—A Tale.” Poe was certain Locke had plagiarized him, but Locke received all the glory for his “Moon Hoax.” (Ironically, Poe’s own hoax included long sections from the aeronaut Thomas Monck Mason’s 1836 account of his balloon voyage from England to Germany.) Poe decided he would do a little self-promotion while outdoing his old enemy: He submitted the hoax to the same paper that had published Locke’s. The paper published the account with glee, completely unaware that it was fake.

According to Poe's report, a balloon called the Victoria held eight people and made the crossing in 75 hours. At the time, it took two weeks to cross the Atlantic by boat, so the potential for a voyage in which “the broad Atlantic becomes a mere lake,” as one of the passengers supposedly remarked, created quite a stir. Poe later claimed that when the Sun first announced the special Extra with details of the fantastic voyage, “the whole square surrounding the Sun building was literally besieged … I never witnessed more intense excitement to get possession of a newspaper. As soon as copies made their way into the streets, they were bought up, at almost any price, from the newsboys.”

Poe included an abundance of scientific detail to give the article an air of authority, from precise measurements of key components, down to the screws and steel wires, to the combined weight of the fictional passengers (1200 pounds). His main characters were also based on real people: Poe named the pilot after Monck Mason, the famed aeronaut whose accounts he had liberally borrowed from.

The report was picked up in the next day's New York Sunday Times (no connection to The New York Times, which had yet to be founded) and Baltimore Sun. Other papers were less convinced of the report's veracity, and seemed to realize that further news should have come up from Charleston. (One contemporary account suggests that Poe himself revealed the hoax by drunkenly boasting about it in front of the crowd at the newspaper’s headquarters.)

Two days after the hoax first appeared, the New York Sun published a retraction. "The mails from the South last Saturday night not having brought a confirmation of the arrival of the Balloon from England ... we are inclined to believe that the intelligence is erroneous," the paper said. However, they added, "We by no means think such a project impossible." Astoundingly, balloonists would not truly accomplish a trans-Atlantic flight until 1978.

Poe believed his little trick would demonstrate his mastery of scientific description and artful writing. He was so assured of his skill, he didn’t seem to realize that publishing known misinformation would hurt his chances of finding work as a journalist—which is exactly what happened.

But the hoax did inspire someone else: Jules Verne later read it and began working on the adventure that would first bring him fame, Five Weeks in a Balloon, published in 1863. That tale was an immediate success, earning him the financial independence that would allow him to go on to write blockbusters such as A Journey to the Center of the Earth and Around the World in Eighty Days. Whether Poe would have appreciated Verne’s achievements, so heavily influenced by his own work, is another matter.

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