Cheryl's Birthday

Vetrix

Vetrix

Well-Known Member
Albert and Benard 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 Benard separately the month and the day of her birthday respectively.

Ablert: I don't know when Cheryl's birthday is, but I know that Benard does not know.
Benard: 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?

Good luck, please do not cheat and if you've heard of this before, do not answer. Thanks.
 
Last edited:
Well, when Albert says the first sentence, it doesn't really help. He only knows the months. But the second sentence that Benard says, gives us a clue. Since Benard knows the day it is on
Vetrix said:
Cheryl then tells Albert and Benard separately the month and the day of her birthday respectively.
Click to expand...
So, he knows the day right? So he only knows the numbers 14,15,16,17,18,19. Also it seems that he secretly knows some numbers hmm. So, the only numbers that could be possibly is 18 or 19, because it was mentioned once. The only months with those numbers is May 19, or June 18. (realizes she did the math wrong...) I'm an idiot....I might as well keep on explaining :expressionless: Ok, we get he has some clue of what months and date of what it could be.
Vetrix said:
Albert: Then I also know when Cheryl's birthday is.
Click to expand...
So, Albert finally guesses the month and date. yay. So, he knows somehow (someone has been eavesdropping) but its Logic. Anywho, he either pick May 19, or June 18 or maybe June 14. Well, I honestly did a bit of probability at that point. Either June 14, or June 18. Well, I honestly picked June 14, but its wrong so its June 18. If I'm wrong then I will hit myself for typing so long for nothing.
 
July 16
1.bernard doesn't know what Albert knows and 18 and 19 appear once which are viable options in Bernard's eyes, so Albert shouldn't know May or June.
2.14 appears both in July and August 14-14=0
3.the remaining is 15,16,17. 16 is the the median.
 
The unknown said:
July 16
1.bernard doesn't know what Albert knows and 18 and 19 appear once which are viable options in Bernard's eyes, so Albert shouldn't know May or June.
2.14 appears both in July and August 14-14=0
3.the remaining is 15,16,17. 16 is the the median.
Click to expand...
You go it right, but unfortunately the 3rd step isn't right. There's no maths involved in this.
 
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