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Cheryl's birthday puzzle.

Posted: 15 Apr 2018, 20:06
by Dreamweaver
When is Cheryl's birthday?
Cheryl tells Albert her birthday is either in May, June, July or August.

She then tells Bernard her birthdate is either 14, 15, 16, 17, 18 or 19.

Albert says he doesn’t know the answer, and he knows that Bernard doesn’t know either.
Bernard says at first he didn’t know, but after hearing what Albert just said, now he does know.
Albert says hearing what Bernard said solves it for him too.

The question was reportedly devised by the Singapore and Asian Schools Math Olympiad (SASMO) for Secondary 3 and 4 students.
Can you work it out?
https://www.youtube.com/watch?v=fSMvPQ2wvW0