Anybody know any good Brain Teasers

carvegio said:
Another one which people usually struggle with

Two ferry boats start at the same instant on opposite sides of the river. One is faster than the other. They cross at a point 720 yards from the left shore on their way to their respective destinations, where each one spends 10 minutes to change passengers before the return trip. They meet again at a point 400 yards from the right shore.

How wide is the river?
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I thought that was going to be a quick thing to work out until I actually sat down and tried it :p

I get the answer as 1760 yards - I can back it up with working if you like.
 
Ut-oh, dare I do it?

Yes :D

A bat and ball costs £1.10. The bat costs £1 more than the ball. How much does the ball cost?

Was that thread ever archived? It should have been...
 
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?
 
Haircut said:
I thought that was going to be a quick thing to work out until I actually sat down and tried it :p

I get the answer as 1760 yards - I can back it up with working if you like.
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I got 1,720 but I did it mainly in my head so I could very easily be wrong!

Edit; No, I just worked it out on paper - it's definitely 1,720!

In fact, if they initially meet at A yards from the left shore, then meet again B yards from the right shore, the width of the river is 3A-B. The time that they spend unloading passengers is irrelevant.
 
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Arcade Fire said:
I got 1,720 but I did it mainly in my head so I could very easily be wrong!

Edit; No, I just worked it out on paper - it's definitely 1,720!

In fact, if they initially meet at A yards from the left shore, then meet again B yards from the right shore, the width of the river is 3A-B. The time that they spend unloading passengers is irrelevant.
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I got the same, but the fact remains that if A is 720 and B is 400 then 3A-B = 1760 :p
 
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?
 
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...


What would the other tribe say if I went this way? :p
 
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