57 replies to this topic

[JFLESH]

what if the guy who said he has the dot first was colorblind?

he'd see the other two have the same dot color and would assume his would be different

[OldDogCage]

Maybe he just wiped his head and looked at his hand?

[johnsl]

I like this one.

The first answer works well - They are stated to be masters of logic - and all hands are raised so obviously anybody who can see a blue dot knows they have a red dot pretty quickly. Nobody does this so the next conclusion is nobody can see a blue dot.

But the second answer is much nicer - the grand master will design a fair test - clearly if the dots are different colours somebody has an advantage.

The nice thing about these solutions is that they don't conflict - but the time delay suggests that the first answer is the intended one.

JSL

[dakotafanningboy]

The man was Hindu.

[Chaos]

If one of them simply covered one of the others dots, he could immediately tell which color his was from the 3rd person because the only dot the third person would see was the first person's.

[AngelicaMary]

Lets say the people were A,B,C.Let C be the one who said that he had a red dot.Now the wise man had to paint at least two red dots else not all would have raised their hands.So he painted one red dot on A's and C's heads.Everyone saw at least 1 dot.C saw that A had red dot and B blue.He thought,"B is raising his hand cause he saw A.But A's also raising his hand so I must have a red dot"Note if all had ed dots nobody would be able to guess at all.

[Linzd21]

if i were one of the three an i saw 2 people with red dots I would immediately know that I too had a red dot on my forhead because the wisest would have to be the one that realized he was being duped.

[scooter3000]

It was painted on. No one said he couldn't touch it while it was still wet. The paint would have been on his finger

[yallways]

Masters of Logic Puzzles I. (dots) - Back to the Logic Puzzles
Three masters of logic wanted to find out who was the wisest one. So they invited the grand master, who took them into a dark room and said: "I will paint each one of you a red or a blue dot on your forehead. When you walk out and you see at least one red point, raise your hands. The one who says what colour is the dot on his own forehead first, wins." Then he painted only red dots on every one. When they went out everybody had their hands up and after a while one of them said: "I have a red dot on my head."
How could he be so sure?

Spoiler for Solution

Masters of Logic Puzzles I. (dots) - solution
The wisest one must have thought like this:
I see all hands up and 2 red dots, so I can have either a blue or a red dot. If I had a blue one, the other 2 guys would see all hands up and one red and one blue dot. So they would have to think that if the second one of them (the other with red dot) sees the same blue dot, then he must see a red dot on the first one with red dot. However, they were both silent (and they are wise), so I have a red dot on my forehead.

HERE IS ANOTHER WAY TO EXPLAIN IT:
All three of us (A, B, and C (me)) see everyone's hand up, which means that everyone can see at least one red dot on someone's head. If C has a blue dot on his head then both A and B see three hands up, one red dot (the only way they can raise their hands), and one blue dot (on C's, my, head). Therefore, A and B would both think this way: if the other guys' hands are up, and I see one blue dot and one red dot, then the guy with the red dot must raise his hand because he sees a red dot somewhere, and that can only mean that he sees it on my head, which would mean that I have a red dot on my head. But neither A nor B say anything, which means that they cannot be so sure, as they would be if they saw a blue dot on my head. If they do not see a blue dot on my head, then they see a red dot. So I have a red dot on my forehead.

AND NOW I HAVE A HEADACHE!!!

[Jimmy]

He just know from the other because the other two also raise up the hand