Can you solve the logic problem that put the Internet in knots?

daniel russell

April 15, 2015 7:03 PM

Are you smarter than a really smart Singapore high school student? If yes, try figuring out Cheryl's birthday.

A logic problem that was posted on Facebook by Singapore television host Kenneth Kong has got the Internet twisted into knots as everyone is trying to find Cheryl's birthday.

The Cheryl's birthday challenge was meant to test high-school students competing in the Singapore and Asian Schools Math Olympiad, held April 8.

The question reads: Cheryl has a birthday, and she doesn't want to share it right away. (Otherwise, we have no challenge to solve.) So she gives her friends Albert and Bernard a list of 10 possible birthday dates:May 15, May 16, May 19, June 17, June 18, July 14, July 16, August 14, August 15 or August 17.

However the wording of the problem is terrible, so here is a clearer version, which makes some of the assumptions more obvious but which does not change any of the underlying logic of the 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!

A brief conversation between Albert and Bernard -- who we assume are not lying for the sake of this problem -- gives the reader enough clues to eliminate nine of the 10 dates and discover Cheryl's birthday.

Well readers can you help us solve this.

When is Cheryl’s birthday?

daniel russell