That Viral Math Problem (Cheryl's Birthday) - Numberphile

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  • Published on: 17 April 2015
  • Simon Pampena gives his take on THAT viral math problem from Singapore.
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  • Runtime : 11:34
  • numberphile Mathematics (Field Of Study) Happy Birthday Mathematical Problem cheryl singapore

COMMENTS: 40

  • David Carter
    David Carter   10 hours ago

    This only works if Albert and Bernard are perfect logicians

  • ThatCreepy Fellow
    ThatCreepy Fellow   2 days ago

    He has really great handwriting and a great way of explaining

  • Ken Dang
    Ken Dang   3 days ago

    question: Jimmy has 1 orange he’s 9 years old

  • Xerox Prime
    Xerox Prime   1 weeks ago

    Last 2 min of explanation sound like mathematical hocus-pocus

  • Dhanush MR
    Dhanush MR   2 weeks ago

    if Albert had said I have 2 options if Bernard doesn't know then I knowThen Bernard says I don't (by these statement both would have got the answer)

  • MockT - bs
    MockT - bs   2 weeks ago

    Can we just appreciate Bernard's smartnessHe does, what took Simon took 8 minutes to explain, in 5 seconds in his head. That is 96-fold the smartness of SimonBruh

  • TheProtean Girl
    TheProtean Girl   2 weeks ago

    So this problem is half mathematical data and half psychoanalysis ahaha I love it! Like mathematical ping-pong one says smth that changes the other.

  • Tido
    Tido   3 weeks ago

    did anyone else get june 17?

  • Richard Kim
    Richard Kim   3 weeks ago

    Finding this again after a few years and being able to solve it feels amazing

  • GDGaur
    GDGaur   4 weeks ago

    Easier way to say Albert: it's slightly more than half.Bernard: it is slightly less than half.Refer the table this joker has made. 😂Gotchaa....

  • GDGaur
    GDGaur   4 weeks ago

    5:25 .... 19(kiss) 😂and Bernard forgot everything

  • sunrevolver
    sunrevolver   1 months ago

    And... From this chain of logic, we know that Albert's guess is 100% correct but bernard's and ours are basically a guess.. As we have the prior assumption that bernard's last statement is true.

  • Baylor Robinson
    Baylor Robinson   1 months ago

    Im not kidding, I did this in my head without knowing the answeri have no idea how

  • Echs Dee
    Echs Dee   1 months ago

    But what if 14 was what Cheryl whispered?

  • Modern Warrior Systems
    Modern Warrior Systems   1 months ago

    I don't understand why he can cross out May and June after the first exchange, because if the birthday was May 15 or 16 it June 17, they still could have had the same first dialogue exchange. Because Albert would have been told June and Bernard told 17, which they still would not have automatically known at the beginning. All three of those dates are within rows and columns with more than one choice.

  • dachducoda
    dachducoda   1 months ago

    I must not have a life because I never heard this problem before until now and I got it first try without the video, don’t see why it was such a trend or issue

  • Eli Jeschke
    Eli Jeschke   1 months ago

    I thought I had it with August 17th because I forgot that the whole months of May and June could be discounted. I gotta work on my logic.

  • Madeleine McCann
    Madeleine McCann   1 months ago

    When u think ur a logic genius cuz u got a random problem right😎

  • Chris P. Bacon
    Chris P. Bacon   1 months ago

    we were never provided with parameters. If what potential month then..... What happened to December October November???? Or it's August 18

  • D.J.
    D.J.   1 months ago

    An important part of the problem is "All they know is that Bernard knows that Albert knows the month and Albert knows that Bernard knows the day but they don't know it together." However, this is an unusual piece of information to know about the problem. In real life applications, how often can we assume to know someone else's full knowledge about a problem, and how often can we consider a person's statements to be truthful? I always consider the possibility that someone else can have more information about a problem that I don't know about. The other person could tell me that they do not know anything else about the problem, and I could trust that person to tell the truth, but, in reality, there is always doubt to what we think to be true.

  • Wesley Pipelayer
    Wesley Pipelayer   1 months ago

    I disagree right around about 10:00. Cheryl told Bernard the date. 15,16, or 17. So now he knows it, and it could be any one of those. There is nothing further to eliminate August. Just because Albert says that he now knows, doesn’t eliminate anything, unless we are all just going off the assumption that he can’t be wrong in his statement (assumption/guess). If and only if we knew that alberts last statement is true, would that ever eliminate anything. So if you did assume that he is correct in his logic, then YOU as an observer could now deduce it down to July 16th. But there is really no way for Albert to deduce it all the way down to that point, unless Bernard gave another statement that could possibly eliminate 2 of the 3 days. So in actuality, it could still be any one of those three dates.So what really happened, is that Bernard knew it to be one of those days. Albert deduces it is not the two in August, because they aren’t a gimme. But there is no reason to believe that it couldn’t have been August 15or 17. As there is no further clue from Bernard. It could still be any one of those three, unless there is some confirmation from Cheryl that his guess was correct.

  • Monsieur Tyrell
    Monsieur Tyrell   1 months ago

    Aaaay! July 16th squad where u at?! Of course only someone with high cancer energy could make an elaborate game out of guessing a birthday.

  • Michele Moneywell
    Michele Moneywell   1 months ago

    Have not heard of the problem. Nice presentation and explanation!

  • Zeineb
    Zeineb   1 months ago

    At 6:51 I don't get why they removed may though

  • TRLittleTim
    TRLittleTim   1 months ago

    Cheryl's parents could have still lost NNN

  • franz009franz
    franz009franz   1 months ago

    i solved this with excel stopping at 2:27. took me about 8 minutes. EZdidn't use the "option" thing in my excel table

  • quasidiem99
    quasidiem99   1 months ago

    More confusing logic question is how a logic puzzle was created with such a disregard for grammar standards.

  • Fallen Spike
    Fallen Spike   1 months ago

    Guess: July 16.Edit: turns out I am right lol

  • Rachael Gong
    Rachael Gong   1 months ago

    i was taught this question in school at 11