This stupid puzzle went viral yesterday. The internet exploded and everyone ended up with different answers. I don’t know how or why this puzzle is so important, but people just wouldn’t shut up about it. There’s only one problem. I love puzzles and I hate it when I can’t solve them. So I’m going to solve this puzzle right now! You might not understand my logic, but that’s okay.
Albert and Bernard just become 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?
Okay, so let’s start with the facts.
Albert knows the month and Bernard knows the day.
Albert: May, June, July, August
Bernard: 14×2, 15×2, 16×2, 17×2, 18, 19
This much is easy. Now is the moment my brain has to start doing something. We can rule out two dates already. May 19 and June 18. These numbers are only mentioned once, if Cheryl had told Bernard the number 18 or 19, Bernard would now know her birthday. The thing is that Albert said that Bernard doesn’t know.
We can immediately assume that June 17 is no longer a possibility either. If Albert knew that June 18 was no longer a possibility and Cheryl told him her birthday month is June he would know the answer as well, but he doesn’t.
Are you still with me?
It’s even simpler than that. Both May and June can be ruled out, because had Cheryl told Albert her birthday month was either May or June, Albert couldn’t have been sure that Bernard doesn’t know her birthday. I mean if Cheryl had said May then Albert would know that there’s still a possibility that Bernard had gotten the number 19. Which goes back to the fact that 19 is only mentioned once and the fact that Bernard doesn’t know when Cheryl’s birthday is.
I really don’t know how to explain this. Does anyone get it?
Only July 14, July 16, August 14, August 15 and August 17 are left.
If Bernard had the number 14, he would still have to guess which month Cheryl was born in, but since he does know, both July 14 and August 14 can be ruled out.
Only July 16, August 15 and August 17 left.
The last step is the same as the one before, but instead for Albert. If Albert had the month August, he wouldn’t have been able to know her birthday, but he does.
The answer is July 16.
Have a nice Wednesday.