a sample Singapore Math Olympiad question(students age 15)

[Za]

Albert and Bernard just became friends with Cheryl, and they want to know when her birthday is.Cheryl gave them a list of 10 possible dates

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

Cheryl then tells Albert and Bernard separately the Month and the day respectively.

Albert: I don't know when Cheryl's birthday is, but I know Bernard doesn't know either.
Bernard: At first I didn't know when Cheryl's birthday was, but now I know.
Albert: Then I also know when Cheryl's birthday is


So when is Cheryl's birthday? (no cheating)

[Za]

Since no one made an attempt to find the logical solution, I'll give the answer.
It is July 16. If you reason through the statements, it will make sense.

[Jawge]

There was once guy called Hari Seldon in the golden age of the forum,
he loved these sort of stuff. he possibly got old and disinterested

Yup "first I did not know when but now I know". ah the key

Interesting.