(Read the problem here)
To get conclusion of the problem, we have three important information from Albert and Bernard’s conversation:
- Albert knows that Bernard does not know
- Bernard knows the answer after point 1 is known
- Albert knows the answer after point 2 is known
So here we have initial options:
May 15 May 16 May 19
Jun 17 Jun 18
Jul 14 Jul 16
Aug 14 Aug 15 Aug 17
Albert at first sure that Bernard does not know the answer. So Albert sure that Bernard was told neither 19 nor 18. It means Albert was not told May or June.
May 15 May 16 May 19
Jun 17 Jun 18
Jul 14 Jul 16
Aug 14 Aug 15 Aug 17
Having told that, Bernard knows the answer. It means he got a unique day of the remaining. Therefore we can eliminate all both 14.
May 15 May 16 May 19
Jun 17 Jun 18
Jul 14 Jul 16
Aug 14 Aug 15 Aug 17
Lastly, it makes Albert knows the answer also. So the only possible reason is Albert was told that Cheryl’s birthday is July.
May 15 May 16 May 19
Jun 17 Jun 18
Jul 14 Jul 16
Aug 14 Aug 15 Aug 17
Therefore, Cheryl’s birthday is July 16.