Results 1 to 8 of 8
  1. #1
    Lazy Idle Couch Potato Heptagon_ru's Avatar
    Join Date
    Aug 2014
    Location
    Russia, near Moscow
    Posts
    983

    Smile The birthday puzzle.

    Maybe some of you haven't seen this logical maths problem. It seems impossible to solve, but actually it's not too hard to find the answer. I have already enjoyed massive holywar among my colleagues, so can't resist to share the puzzle with you.

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

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

    Cheryl then tells Albert and Bernard separately the month and the day of her birthday, respectively.

    Albert: I don't know when Cheryl's birthday is, but I know that Bernard does not know, too.
    Bernard: At first, I didn't know when Cheryl's birthday is, but I know now.
    Albert: Then I also know when Cheryl's birthday is.

    When is Cheryl's birthday?

  2. #2
    Cake! InsaneJ's Avatar
    Join Date
    Jan 2012
    Location
    Cakeville
    Posts
    4,617
    Blog Entries
    21
    Logic puzzles hurt my brain

    Answer....
    Spoiler!

  3. #3
    Lazy Idle Couch Potato Heptagon_ru's Avatar
    Join Date
    Aug 2014
    Location
    Russia, near Moscow
    Posts
    983
    Wow, that was quick. Oh, cmon, put the answer under spoiler at least )))))

    If it hurts, it is still present, and it's great. ))

    At work we (after 3 days) still can't convince one colleague about the answer and about the logic to get it. Every day it gets very emotional ))

  4. #4
    Well I officially fail at these things. I can't figure it out, even though J already said the answer, I have no idea how it go to that answer xD
    Watch me live, or not, up to you... https://www.twitch.tv/legendofair

  5. #5
    Lazy Idle Couch Potato Heptagon_ru's Avatar
    Join Date
    Aug 2014
    Location
    Russia, near Moscow
    Posts
    983
    One of the explanations:
    http://www.theguardian.com/science/alexs-adventures-in-numberland/2015/apr/13/how-to-solve-albert-bernard-and-cheryls-birthday-maths-problem

    For a small hint you can read only the beginning of the explanation.

    Personally I'm bad too, and in this case I even didn't have a chance to solve it, because the initial post where I read that was styled more like a joke, so I thought it was a joke And only after reading a comment with the explanation .... Well, since it was also a bit hard to get the idea from the explanation, at least some profit for the hurtless matter inside my head ))
    Last edited by Heptagon_ru; 16th April 2015 at 16:08.

  6. #6
    Cake! InsaneJ's Avatar
    Join Date
    Jan 2012
    Location
    Cakeville
    Posts
    4,617
    Blog Entries
    21
    The solution lies in the order in which Albert gains more information from his conversation with Bernard.

    What does he know already? What knowledge does he gain by Bernard first not knowing, and then knowing because Albert didn't know? Because Albert didn't know, one scenario was eliminated for Bernard, which one? What does that leave him with?

  7. #7
    Quote Originally Posted by Heptagon_ru View Post
    Maybe some of you haven't seen this logical maths problem. It seems impossible to solve, but actually it's not too hard to find the answer. I have already enjoyed massive holywar among my colleagues, so can't resist to share the puzzle with you.

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

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

    Cheryl then tells Albert and Bernard separately the month and the day of her birthday, respectively.

    Albert: I don't know when Cheryl's birthday is, but I know that Bernard does not know, too.
    Bernard: At first, I didn't know when Cheryl's birthday is, but I know now.
    Albert: Then I also know when Cheryl's birthday is.

    When is Cheryl's birthday?
    Just over a year later, but still entertaining Thank you from me and my friends. It was really funny Tea break on a Friday afternoon. We've solved it without cheating. If someone has not seen it, try to solve it Good luck!

  8. #8
    Spoiler!
    Last edited by latyper; 17th May 2016 at 21:55.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •