Cheryl's Birthday: Singapore's maths puzzle baffles world
1–10 of 16 posts
Re: Cheryl's Birthday: Singapore's maths puzzle baffles world
#2I think there are two solutions. The video in the link gives one, the other is June 17. Supposing Albert knows the day, his statement eliminates June 18 and May 19. Bernard claims to know the answer, which can only be June 17. Albert does the same logic and reaches the same conclusion.
Re: Cheryl's Birthday: Singapore's maths puzzle baffles world
#3I think there are two solutions. The video in the link gives one, the other is June 17. Supposing Albert knows the day, his statement eliminates June 18 and May 19. Bernard claims to know the answer, which can only be June 17. Albert does the same logic and reaches the same conclusion.
I am not sure that is true. If albert knows bernard doesn't know the day at the beginning, it can't be june since the number 18 would be uniquely identifiable as june 18 for bernard from the beginning.
Re: Cheryl's Birthday: Singapore's maths puzzle baffles world
#4Re: Cheryl's Birthday: Singapore's maths puzzle baffles world
#5I think there are two solutions. The video in the link gives one, the other is June 17. Supposing Albert knows the day, his statement eliminates June 18 and May 19. Bernard claims to know the answer, which can only be June 17. Albert does the same logic and reaches the same conclusion.
But, Albert doesn't know the day at first. If Cheryl had told him "June" he would not know that Bernard does not know her birthday.
Re: Cheryl's Birthday: Singapore's maths puzzle baffles world
#6My logic for this puzzle goes as follows:
1) Albert knows Bernard cannot know the answer immediately. As 18 and 19 are days that only appear once, the month must not contain those dates, so May and June are eliminated.
2)Bernard is able to identify the month based on knowing it can't be june or may and based on his date. Therefore Bernard cannot have had the number 14. He must have 15,16, or 17.
3) Knowing it is 15, 16, or 17 uniquely identifies the date for albert. Since august has 2 options left, it must be july, and the only date available is July 16.
This is a tricky problem, but it is one that is fairly straightforward to approach step by step. Definitely appropriate for advanced students at age 15. The problem reminds me of the question about how many people on an island have blue/brown eyes.
I haven't done logic problems in a long time, so I may have erred and would welcome alternative interpretations.
Re: Cheryl's Birthday: Singapore's maths puzzle baffles world
#7I think there are two solutions. The video in the link gives one, the other is June 17. Supposing Albert knows the day, his statement eliminates June 18 and May 19. Bernard claims to know the answer, which can only be June 17. Albert does the same logic and reaches the same conclusion.
If there are two solutions, then there are zero solutions.
Re: Cheryl's Birthday: Singapore's maths puzzle baffles world
#8I think there are two solutions. The video in the link gives one, the other is June 17. Supposing Albert knows the day, his statement eliminates June 18 and May 19. Bernard claims to know the answer, which can only be June 17. Albert does the same logic and reaches the same conclusion.
Albert doesn't know the day. The problem states that Albert and Bernard know the month and day respectively.
Re: Cheryl's Birthday: Singapore's maths puzzle baffles world
#91. Albert has July, so he knows all the days Bernard could have been given have duplicates. Thus, he knows Bernard doesn't know the birthday yet.
2. Bernard hears this and knows Albert is holding on to either July or August. He holds a number that is unique within these 2 months. That is why he now knows the birthday.
3. Albert now knows that Bernard knows, and thus has a day that is unique between July and August. Which means it cannot be 14.
4. So among July 16, August 15, and August 17, the only way Albert can know for sure is if he is holding on to July.
Therefore July 16.
Re: Cheryl's Birthday: Singapore's maths puzzle baffles world
#10I think there are two solutions. The video in the link gives one, the other is June 17. Supposing Albert knows the day, his statement eliminates June 18 and May 19. Bernard claims to know the answer, which can only be June 17. Albert does the same logic and reaches the same conclusion.
Albert does not know the day, he knows the month. Alberts statement eliminates all June and May dates because he says he "Know thats Bernard doesn't know" before Bernard says he didn't know.