Players A and B both have got the number 12 written on her forehead. Everyone sees the number on the front of the other but does not know the own number. The game master tells them that the sum of their numbers is either 24 or 27 and that this numbers are positive integers (thus also no zero).
Then the game master asks repeatedly A and B alternately, if they can determine the number on her forehead.
A: "No".
B: "No".
A: "No".
B: "No".
A: "No".
....
After how many "no"s does the game end, if at all?
the answer
[tab]A. His number is 12? It adds up to either 24 or 27. Mine is either 15 or 12.
I do not know what my number is.
B. A does not know what his number is. His number is 12 though. He must be thinking
his number is 15 or 12. But if his number is possibly 15, that means my number is not 15.
So my number is 12.
So it should only be after 1 no will the game end.[/tab]
You are wandering through the wilderness in the middle of the night and come up to a fork in the path.
There you meet two old men sitting on a large wood stump.
Legends tell that one of these old men speaks only the truth and that the other one always lies.
One of these paths leads to certain death while the other grants safe passage home. Both of those old men know about those two paths and which leads to which destiny.
You get to ask one of these two men one question.
Try to figure out, with this one question, asking one of the two men, which path is safe.
[tab]If you not gonna try doing it on your own, at least google it…[/tab]
[tab]I ask one of the men which path the other one would show me as being the safe one. The liar would lie and tell me the wrong path, because this is not what the other man would say. The truth teller would tell the truth and also show me the wrong path, because this is the lie which the other one would tell me. So both would tell me the wrong path and I would take the other one.[/tab]
[tab]I didn’t google it! But I knew the riddle :-" .[/tab]
I tried to reconstruct this riddle with a friend a few years ago and even knowing roughly the key idea behind the solution* it still took quite some time to do so.
[tab]that the question has to involve the other man in some way or form[/tab]