hello there.: 'When is Cheryl's birthday?' The maths problem set for teenagers that has baffled the world.

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?

Just when you thought math couldn't get any harder.

A TV presenter in Singapore recently brought up a math problem that has been driving the Internet crazy.

At first, the problem seems impossible to solve. But once you use some logic, the solution is actually rather simple. Rattle your brain — or phone a friend —before you look at the solution below the picture.

The solution, courtesy of Singapore's Study Room:

First we need to figure out if Albert knows the month or the day. If he knows the day, then there is no chance that Bernard knows the birthday, so it must be that Albert knows the month.

From the first statement, we know that Albert is sure that Bernard doesn't know the birthday, so May and June should be ruled out (the day 19 only appears in May and the day 18 only appears in June). In other words, if Albert had May or June, then he cannot be sure that Bernard doesn't know, since Bernard could have had 18 or 19.

Following that statement, Bernard knows that May and June are ruled out.

Then, Bernard is able to know which month it is. So it must be either July 16, August 15 and August 17 (not 14th as then he can't know).

Since Albert subsequently can also be sure of the date, he must know it's July. If it's August, he can't be sure as there is August 15 and 17.

So the answer is July 16.

The question was originally thought to be posed to fifth graders but was later clarified to be for 14-year-olds competing in the Singapore and Asean Schools Math Olympiads (SASMO). Organisers of SASMO said the question was set to filter out the most intelligent of participants
It was the first ever recorded leak from the competition's booklets and will be replaced by the time Cambodia runs the competition.