When is Cheryl's birthday? You might think that this is a straightforward question, but it has ignited an internet furor that may just be the math equivalent of the black and blue/ white and gold dress debate.

Kenneth Kong is a math teacher from Singapore, and he when he posted a math problem on Facebook on April 10, it quickly went viral. Although the problem was intended for high school Math Olympiad students, many adults struggled with the answer.

Are you smarter than the high school students in Singapore? Here's the original problem:

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?

Having trouble figuring it out? You're not alone! Netizens have come up with a wide range of responses, including some humorous ones:

  • Imagine Cheryl ordering a pizza. Calls 2 separate places, tells one the address and the other the toppings. Goes hungry. #CherylsBirthday @YukonTeddy
  • Just add Cheryl on Facebook and you'll be notified when her birthday comes along. #cherylsbirthday — @chiiiiing
  • I Don't Care When Your Birthday Is Cheryl And You're Not Getting A Present. #cherylsbirthday — @Q107Toronto
  • I suggest that Albert and Bernard find a new friend who is not Cheryl. #cherylsbirthday  @NithiyaSaher

If you want to see if you got the question right, The New York TimesThe Washington Post, and CNN all posted breakdowns on how to solve the problem.

Even if I don't know when Cheryl's birthday is, she sounds like a big jerk, to be honest.


See Cha Seung Won and Lee Yeon Hee in the gripping historical series Hwajung: