A question on a quiz for teenage mathletes proved so tricky for Singapore newscaster Kenneth Kong that he posted it to Facebook to find a definitive answer. Now the problem has driven the entire country mad, and it's spreading to the rest of the world.
So, what's the answer? IS there an answer? When is Cheryl's goddamn birthday?!
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?
One possible solution is that Albert and Bernard are no longer friends with Cheryl, because nobody wants to chill with some wily human sphinx who introduces herself by presenting inscrutable logic problems.
Cheryl: "What is that which in the morning goeth upon four feet; upon two feet in the afternoon; and in the Evening upon three?"
Bernard: "Come on, Albert. Let's bounce."
Albert knows that Bernard can't know the answer just by knowing the day. So we have to rule out May and June, both of which have days (the 18th and 19th) unique to them.
Knowing those months have been ruled out, Bernard's knowledge of the day suddenly gives him the answer. How?
Well, it can't be the 14th. It's the only repeated number, and it wouldn't give him any information about the correct month. That leaves only three choices: July 16, Aug. 15, and Aug 17.
Now we've exhausted all of Bernard's information about the day, and we still don't have an answer. This is where some people, like Jianwen, probably gave up and declared the problem a trick. Bernard seemingly doesn't have enough information to answer the question.
Hold up, though. Bernard knows one more thing: that Albert got the correct answer by knowing the month.
Albert couldn't do that if Cheryl's birthday were in August, because there are still two August dates for him to choose from. And that means there's only one possible birthday left: July 16.
Happy fucking birthday, Cheryl, you slippery enigmatrix.
This doesn't have everyone convinced, though. In fact, the Singapore and Asian School Math Olympiads have released a statement in response to a popular argument that the answer is actually August 17. (It's not, but the reason is a bit tricky.)
Did you get it? Will you have the honor of paying tribute to the winged lion on the anniversary of its birth, or will you be subject to its tremolous, roaring laughter in your nightmares evermore? The stakes are high for young Singaporean mathletes!