Anybody know any good Brain Teasers

Arcade Fire said:
You have a stick one metre long, and the width of one ant. You randomly place a hundred ants on it, either facing forwards or backwards at random. When the ants start walking, they always move at one metre per minute. When two ants collide, they both turn around and start walking in the other direction. When an ant reaches the end of the stick, it falls off.

What's the longest you'd have to wait to be sure that all of the ants had fallen off the stick?
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Bah, you guys are lame. My friends at uni worked this one out in minutes!

Since all of the collisions between ants are elastic (i.e. the ants move away from each other at the same speed as they came in) then you might as well ignore the collisions altogether and have the ants walking through each other. Then all you have to do is wait for an ant at one end of the stick to make it to the other end - and the answer is obviously one minute.
 
Freefaller said:
A man is lost in the desert - he has run out of supplies and knows that there is a town with food and water waiting for him. However he comes to a fork in the road with a signpost giving 2 directions. One of them to the little oasis which he needs/wants to get to, the other to the cannibal city. This city has 2 cannibal tribes, one tribe always tells the truth, and the other always lies. These cannibals are very logical and ethical and will only eat stupid people that cannot solve this puzzle! ;)

At this fork leaning on the sign post (which was placed there by one of the tribes, which one we don't actually know) is a cannibal. The cannibal sees the parched man approaching and offers help but at a cost. He allows the man to ask one question only. From this answer he must decide which direction he must go in to go to the oasis.

What question should the man ask if he is to get to where he wants to go?
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b
alternative answer - which way to YOUR tribe?

THe liar will lead you to the 'truth' tribe, the truth teller will lead you to the 'truth' tribe
 
carvegio said:
The warden of a prison wants to give his 10 prisoners a chance to redeem
themselves. He approaches them one evening when they are all sitting
together and relaxing and tells them the following:

"Tomorrow morning I am going to stand all of you in one line, facing the
same way one behind the other. I will place the shortest in the front and
the tallest at the end of the line so each of you can see all people ahead
of you, but none behind you.

Then, I will proceed to place a hat on each of your heads. Each hat will
either be black or white in colour, but you will not know how many of each
there are (they could be all black, or even all white). Moreover, you will
NOT be able to see the colour of your own hat, but you will be able to see
the colours of all the hats in front of you. So the tallest person will see
9 hats, the next 8 and so on. At this point, I will start from the back (the
tallest) and ask each of you the colour of your own hat. If you are able to
tell me the colour of your hat correctly, you are free to go.
If not, you stay right here in jail.

Let me add, that when you are asked the question, all you can say is "black"
or "white". No other word or signal is allowed. Everyone will be able to
hear your answer, but only the ones behind you will know if it was correct."

So the prisoners' task is to think of a strategy which will allow the
maximum number of them to get out of there. For example, if the 10th person
(the tallest) agrees to call the 9th person's hat colour when his turn
comes, then the 9th person can be assured that he will get out. Of course,
in this case, the 9th person can no longer make such a promise to the 8th
because if the 8th person's hat is a different colour than his own, what
will he call when his turn comes by: his own colour to get out of jail or
the 8th person's colour? So such a strategy will clearly not save more than
5 people (10 tells 9, 8 tells 7 etc.) The question is, can we do better? Is
there a clever strategy that can assuredly get more people out of that
prison in this game?

Hint: YES there is! =)
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Whats the answer to this one???
 
Melon said:
Whats the answer to this one???
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I looked that one up because it was confusing me.

It's all in what the first guy says. The prisoners must decide that if the first guy says "black" he means he can see an even number of black hats, and if he says "white" he means an odd number of black hats. The next person can then count how many black hats there are, and based on the first answer, can deduce whether his hat is black or white, and give the correct answer. The next guy then counts the hats in front, counts or ignores the answers of any previous people who said black (barring the first guy) and can then figure out whether his hat is black or white. This way, they can save all but the first guy, and he has a 50% chance of being safe.

Example:

Back Front
WBWWBBBWBB

The first guy, at the back, counts and can see 6 black hats. This is even, so he says black. Sadly, his hat is white, so he dies.
The second guy, then counts and can see 5 black hats in front of him. He knows that the guy behind him said there was an even number, so he knows his hat must be black. He says black and goes free.
The third guy then counts the black hats in front of him, and sees five. He knows the guy behind him had a black hat, so that makes six. This is even (as the first guy said), so his must be white. He says white and goes free.

And so on and so forth to the front of the line. Using this method, they expect to free at least 9 people.
 
Here's another good hat one:

A prison guard has three prisoners, called Shadrach, Meshach and Abednego. It's coming up to Christmas, and he's feeling generous, so he decides to play a game with his prisoners and perhaps let some of them go free.

He says to his three prisoners "I have five hats. Two are black, and three are white. I will place a hat on each of your heads. You will be able to see each others hats, but not your own. I will ask you each in turn for the colour of your hat. You can say only 'black' or 'white'. If you can tell me the colour of your hat, you can go free. If not, you stay in prison."

He blindfolds his prisoners, puts a hat on each of their heads, then takes off their blindfolds. He asks Shadrach what colour his hat is. Shadrach looks at the other two prisoners, but he has no idea and he tells him he doesn't know. He turns to Meshach and asks him what colour his hat is. Meshach looks around, but he too has no idea.

The prison guard looks at them and says "Well, this is very sad! You must all stay in prison!". Abednego says to the guard "Sir, this is unfair! You didn't ask me what colour my hat is?". The guard laughs a little and says "Why, of course not Abednego! You are blind!". Abednego then tells the guard with absolute certainty the colour of his hat, and the guard lets him go free.

What colour was Abednego's hat? How did he know?
 
vonhelmet said:
What colour was Abednego's hat? How did he know?
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Took me a couple of minutes, but I got there.

If neither of the first two men can be sure of their hat colour, it means that they can either see one black and one white hat, or two white. If they'd seen two black hats they could be sure theirs was white. Abednago knows his hat is white because since neither of the others could be sure, they either all have white hats on, or his companions both have black hats on.
 
Belmit said:
Took me a couple of minutes, but I got there.

If neither of the first two men can be sure of their hat colour, it means that they can either see one black and one white hat, or two white. If they'd seen two black hats they could be sure theirs was white. Abednago knows his hat is white because since neither of the others could be sure, they either all have white hats on, or his companions both have black hats on.
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Close enough :)

Basically if he had a black hat on, then one of the previous guys would have figured it out.
 
vonhelmet said:
What colour was Abednego's hat? How did he know?
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If Shadrach saw two black hats, he would know his was white, and would answer. Similarly for Meshach.

If either saw a black and a white hat, or two white hats, they would not know the colour of their hats.

Abednego will say that he has a white hat, as the silence of the others means they both see at least one white hat.

Then they were all thrown into a furnace. Hats and all.
 
Freefaller said:
A man is lost in the desert - he has run out of supplies and knows that there is a town with food and water waiting for him. However he comes to a fork in the road with a signpost giving 2 directions. One of them to the little oasis which he needs/wants to get to, the other to the cannibal city. This city has 2 cannibal tribes, one tribe always tells the truth, and the other always lies. These cannibals are very logical and ethical and will only eat stupid people that cannot solve this puzzle! ;)

At this fork leaning on the sign post (which was placed there by one of the tribes, which one we don't actually know) is a cannibal. The cannibal sees the parched man approaching and offers help but at a cost. He allows the man to ask one question only. From this answer he must decide which direction he must go in to go to the oasis.

What question should the man ask if he is to get to where he wants to go?
Click to expand...


If I asked a member of the tribe you don't belong to which road I should take to get to the castle, what would he say?

then do the opposite

gah didn't realise there where TWO pages?!?!?!!!
 
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