This question has been circling around the web recently though I remember a similar question (if not the exact same one) being a major topic a few years back as well.
It appears that this is a primary 5 question from a school in Singapore and people are debating over the answer. There is one particular site claiming the answer is 17 August and comes up with a seemingly logical explanation. If the conversation starts with Bernard saying that he doesn’t know the answer, then the 17 August explanation is correct. However, this is not the case. Let me explain the solution below.
Here are the possible dates:
May 15 May 16 May 19
Jun 17 Jun 18
Jul 14 Jul 16
Aug 14 Aug 15 Aug 17
The conversation begins with Albert (who knows the month) saying that he doesn’t know the answer and that he is also certain that Bernard (who knows the date) doesn’t either. Albert can only say this if the month he knows has all dates occurring more than once (i.e. 14, 15, 16, and 17).
In other words, if the month is May, then Albert cannot make this statement since Bernard could possibly know the answer if the date is 19. So we know it is not in May.
Remaining possible dates:
Jun 17 Jun 18
Jul 14 Jul 16
Aug 14 Aug 15 Aug 17
Likewise, if the month is June, then Albert cannot make this statement either since Bernard could possibly know the answer if the date is 18. So we know it is not in June.
Remaining possible dates:
Jul 14 Jul 16
Aug 14 Aug 15 Aug 17
At this point, Bernard knows that the month can only be July or August and he says he now knows the answer. Which means, the date cannot be 14, since it occurs twice in the remaining possible dates.
Remaining possible dates:
Jul 16
Aug 15 Aug 17
Looking at the dates above, regardless of the date being 15, 16, or 17, Bernard will know the answer since they all only occur once. But, for Albert to also know the answer, it cannot be in August, since there are still two options.
Hence, the answer is July 16.
I hope this is not confusing.
