http://www.nzherald.co.nz/world/news/article.cfm?c_id=2&objectid=11432276 (http://www.nzherald.co.nz/world/news/article.cfm?c_id=2&objectid=11432276)
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, May 16, May 19
June 17, June 18
July 14, July 16
August 14, August 15, August 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 don't know when Cheryl's birthday is, but I know now.
Albert: Then I also know when Cheryl's birthday is.
So when is Cheryl's birthday?
When I read the question I was confused. When I read the answer I was only more confused (see link for answer), I don't understand how they can draw those conclusions.
First we need to figure out if Albert knows the month or the day. If he knows the day, then there is no chance that Bernard knows the birthday, so it must be that Albert knows the month.
This doesn't make any sense to me, if Albert knows that Bernard doesn't know, then Bernard must only know the months, as they are not unique. Which means Albert knows the date.
From the first statement, we know that Albert is sure that Bernard doesn't know the birthday, so May and June should be ruled out
I was able to rule out June, but what is the logic for ruling out May?
Your challenge is to explain the solution to me so that I understand.
Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively.
Wouldn't that mean that Albert knows the month, and Bernard knows the day?
"First we need to figure out if Albert knows the month or the day. If he knows the day, then there is no chance that Bernard knows the birthday, so it must be that Albert knows the month."
.... be a bunch of bullshit written by someone who heard the riddle at a bar the other night?
I'm trying to figure this shit out. No matter what, it is impossible for you to figure out an answer. Someone smart write why other solutions are wrong.
How the fuck do you rule out May or June?
So Albert is told the month.
If he was told May, possible solutions are 15 , 16 or 19
If he was told June, 17 or 18
If he was told July, 14, or 16
If he was told August, 14, 15, 17
Then burnt-ass Bernard is told the day.
If he was told 14, He knows it's July or August
If he was told 15, May or August
If he was told 16, May or July
If he was told 17, June or August
If he was told 18, it would be June
If he was told 19, it would be May.
So looking at that, On the fact that Bernard hasn't jumped up screaming that he "figured" it out, Albert can say "Well it's not May 19th or June 18th". Thank god for that because it has brought us so much closer to no where. Albert already knows the month, so you can't "rule" out anything based on Bernadds reaction. Even if you did rule out those 2 exact dates, Who is to say that June 17th, or May 15th or 16th aren't possible answers? Albert doesn't know the day so he can't assume that because asshole Bernard isn't crying with tears of joy, doesn't mean that it's not May 18th or June 17th.
I don't believe this is a riddle.