Viral math question

The math question was posted by Hello Singapore TV host Kenneth Kong on his Facebook page with the caption: "This question caused a debate with my wife."  The question went viral across the country with both adults and teenagers grappling with the answer. It made the way on Twitter and Reddit eventually rising to the attention of the Australian Federation of International Students.

The Singaporean math curriculum includes a lot of these logic type puzzles and their math program is world renowned and emulated globally but this puzzle worried parents who believed it is too difficult for level P5 (fifth grade).

The Atlantic goes on to discussing the comparative low US standing in math and why. By their analysis we concentrate more on rote learning than they do and to test, according to Atlantic, while the Singapore method teaches deep layered understanding of math and logic problems with emphasis on how they arrive at solutions.

This problem is one such layered logical problem. You have to have a couple of aha's in a row to solve it, three of them actually.

Mothership Singapore investigated. Turns out it was really a 9th grade logic-math question, not a 5th grade question. But still a very good logic question that shows what these kids are up to.

Albert and Bernard meet a girl named Cheryl, and after marveling how their names alphabetize conveniently for maths problems, the boys asked Cheryl the date of her birthday. She plays her little girlish games and tells Albert the month and she tells Bernard the day, and tells both boys it can be any of these 10 days.

May 15  May 16  May 19
June 17  June 18
July 14   July 16
Aug 14   Aug 15  Aug 17

Albert says he does not know Cheryl's birthday but neither does Bernard.
Bernard says he did not know the birthday at first, but now he does know Cheryl's birthday.
Albert says, now that Bernard confirms that he knows, he too know Cheryl's birthday.

Solution at Mothership.