That Viral Math Problem (Cheryl's Birthday)  Numberphile
 Published on: 17 April 2015
 Simon Pampena gives his take on THAT viral math problem from Singapore.
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 numberphile Mathematics (Field Of Study) Happy Birthday Mathematical Problem cheryl singapore
COMMENTS: 40

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 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 96fold the smartness of SimonBruh

TheProtean Girl 2 weeks ago
So this problem is half mathematical data and half psychoanalysis ahaha I love it! Like mathematical pingpong one says smth that changes the other.

Richard Kim 3 weeks ago
Finding this again after a few years and being able to solve it feels amazing

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....

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

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 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 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.

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. 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 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 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.

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 1 months ago
More confusing logic question is how a logic puzzle was created with such a disregard for grammar standards.
This only works if Albert and Bernard are perfect logicians