The problem of mathematics that shocked the world

A television presenter in Singapore has created a virtual zallamahi after posting a mathematical problem, which is submitted to the country's children.

At first glance, he seems to confound, but of course it is solvable. However, the problem has received thousands of comments and is scattered everywhere, especially when it was thought that was the 10-year-old, writes "The Independent".

Presenter Kenneth Kongo clarified that the problem is for 14-year-old in Maths Olympiad Singapore Schools and Asia. However, the adults introduced in the game. Yes you can choose the exercise?

Here it is:

Albert and Bernard have become friends with Cheryl and want to discover her birthday. Cheryl gives them 10 possible date: 15 May 16 Maj 19 May 17 June 18 June 14 July 16 July 14 August 15 August 17 August.

Cheryl says both, separately, month and day of her birth. 

Albert: I do not know when Cheryl's birthday, but also know that neither Bernard knows.
Bernard: At first, I did not know when the Cheryl had a birthday, but now I know.
Albert: So, I know where Cheryl's birthday. So, when is her birthday?

Solving the problem

First, we must find if Albert knows month or day. If he knows the day, it is unlikely that Bernard knows birthday, to have that Albert knows month.From the first sentence, we know that Albert is certain that Bernard did not know the birthday, on May and June should be excluded (19 appear only in May and 18 in June alone).

So, if you know Albert May or June, he can not be sure that Bernard did not know, as Bernard may have been from 18 or 19. From that sentence, knows Bernard May and June are excluded.

Then, Bernard can know the month. It may be 16 August, 15 August and 17 August.

As Albert can not be sure of the date, he must know that it is July. If it is August, he could not be sure if it is 15 or 17 August.
So the answer remains 16 July. Do you agree?