Here's how to solve 'Cheryl's birthday...

Georgia Tech professor and mathematician Matt Baker explains the answer to 'Cheryl's birthday' problem that has been stumping people all over the world.

[DerpiusDerp]

Wow just wow Those High schoolers should get a prize

[SariennMusic]

Wayyy too difficult. This is why I never ever do riddles. I definitely don't have a genius IQ. Listened to the vid three times and it still doesn't make sense.

[WaqasAhmad-votg]

The thing that is not explained here is that if Albert does not know the dates and only knows the months how can he tell Bernard that he does not know either.

[pbierre]

May 15th could well be Cheryl's birthday.   She tells Albert "May".  She tells Bernard "15".   Albert can only conclude that it's not May 19th, since (by common sense about solving puzzles) Bernard would have announced "I solved it" had he been told a 19.

But, Albert does not know whether it's May 15 or May 16, and is stating the obvious by saying that "I don't know".   He can assume Bernard was told a "15" or a "16", and thus has 2 month possibilities that can't be resolved.  No new information is conveyed by Albert saying that Bernard does not know the answer.

So, if May 15th is whispered, the boys cannot arrive at the birthday.

This disproves the assertion that all of May must be ruled out.

If you start with a decision tree, with all 10 birthdays as possible scenarios, only 2 scenarios may be solved definitively.  All the other 8 lead to unresolvable ambiguity. 

The statements by Albert and Bernard about what the other one knows or doesn't know are totally lacking in common sense.   People do not have the ability to look into each other's brains and obtain unequivocal state information.

[johnsobj]

Everyone should stop acting so impressed.  Slow down and think about it.  Really isn't that hard.  Problem is too many people get "starry eyed" when they see a word problem.

[heuningkai]

Boiiii the host on the news has a point i was thinking of the same thing HAHAHAHA

[bo_jelin]

Ok but why does Albert know that Bernard doesn't know??

[gertaajazi]

As Bernard is the one that knows the date..there is no need for step three. There is only one 16 left :D

[parmetza]

MY NAME IS CHERYL And my birthday is November 14!!!

[IDNeon]

This is the wrong answer because both Albert and bernard have the same list, the variables are globally known.

Because of this Albert knowing Bernard doesnt know only informs Albert that Bernard cannot have been given the days 18 or 19.

It is true that Albert knows Bernard doesnt know even when May 15th or 16th is possible.

If we consider that all conditions must be true or false and continue to eliminate may, then Albert can know the birthdate before Bernard which logically contradicts the word problem.

The actual answer is August 17th, because only then while Albert still thinks it can be May, June, July or August, because albert doesnt know the day, this tells bernard because we know Albert doesnt know the correct date that it cannot be June 17...because there is only one day remaining for that month. Albert would know it is june 17 if he knew it was june.

Now because bernard knows it is 17 it must be August 17.

This solution is correct for the given logic.

[abhishekdsl]

Does'nt make any sense. Need a better explanation.