EntropySink
Nothing & Everything => Open Discussion => Topic started by: joshdick on April 11, 2005, 04:24:09 PM
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There are two lengths of rope.
Each one can burn in exactly one hour.
They are not necessarily of the same length or width as each other.
They also are not of uniform width (may be wider in middle than on the end), thus burning half of the rope is not necessarily 1/2 hour.
By burning the ropes, how do you measure exactly 45 minutes worth of time?
Give a barrel with an indeterminate amount of water in it, how can you discern whether it is exactly half-full without measuring it conventionally?
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1) Use a watch?
2) Cool it down and then bring it back to warm temp... look for a condensation line.
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1) You forgot your watch that day. That's why you're burninating ropes to measure time.
2) There's an easier way than that.
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There are two lengths of rope.
Each one can burn in exactly one hour.
They are not necessarily of the same length or width as each other.
They also are not of uniform width (may be wider in middle than on the end), thus burning half of the rope is not necessarily 1/2 hour.
By burning the ropes, how do you measure exactly 45 minutes worth of time??
Seems to me that you could cut one rope down the entire length of the rope, resulting in two half-ropes that would burn in 30 minutes. Cut one of those halves in half (once again, down the entire length), and you'd have a half-rope that would burn in 30 minutes and two quarter-ropes that would burn in 15 minutes. Start the half-rope, and start a quarter rope when the half-rope is finished.
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1. Start burning one rope and count the exact number of bars of "Stairway to Heaven" that you can hum in the time the rope takes to burn. (repeating the song as necessary). Now re-hum 3/4 of the total amount you hummed in the first place and you have exactly 45 mins (be sure to keep your tempo even!). hah, i didnt even need the second rope.
2. Didnt whats his face do that in lethal weapon?
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Seems to me that you could cut one rope down the entire length of the rope, resulting in two half-ropes that would burn in 30 minutes. Cut one of those halves in half (once again, down the entire length), and you'd have a half-rope that would burn in 30 minutes and two quarter-ropes that would burn in 15 minutes. Start the half-rope, and start a quarter rope when the half-rope is finished.
Except for the fact that he said 1/2 the rope does not mean 1/2 the time.
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pianorain: wouldnt the rope fall apart if you cut it length wise? I think my solution is much more feasable.
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Ober's right about that.
Perspective, but what if I can't remember all the words? ;)
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> Perspective, but what if I can't remember all the words?
Then you're a horrible horrible person.
There are lots of ways to do the second one. I prefer pouring the contents into a barrel with exactly half the volume of the first.
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Ober's right about that.
Hmm...not the way I read the rules.They also are not of uniform width (may be wider in middle than on the end), thus burning half of the rope is not necessarily 1/2 hour.
By cutting the rope length-wise instead of the usual manner, I'm taking care the "not uniform width" problem. Both halves would be the same.pianorain: wouldnt the rope fall apart if you cut it length wise? I think my solution is much more feasable.
Bah...that's an exercise left for the reader. ;)
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But alas, Govtcheez, you have but that one barrel.
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new try:
1)
shit... I cheated and looked it up on the net. Nevermind.
2) I didn't look this one up, but if you measured the height of the barrel and the height of the water inside, you could tell.
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Given a barrel with an indeterminate amount of water in it, how can you discern whether it is exactly half-full without measuring it conventionally?
Cut a hole in the barrel at the half-way point. If water leaks, then it's more than half-full (for a while, anyway). Then choose a solution:
#1) Place a rock in the barrel (preferably small). If water leaks out, then the barrel was half-full or you used too large of a rock. If water does not leak out, then the barrel was not half-full.
#2) Add water until water begins to leak out. Wait until the water has stopped. Now the barrel is half-full.
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But alas, Govtcheez, you have but that one barrel.
Hey, fuck you, you don't know what I have. You think just cause I'm poor I don't have a barrel?
PS This "brainteasers" are always fucking dumb because there're a million possible answers, but only one is the "correct one", and the only way you know that is if you heard it before. The best ones like this are the dead fisherman and the man that hangs himself.
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Tilt the barrel until you see the bottom. If you are wet, the barrel was more than half-full. If you are dry and the water reaches the top edge of the barrel it was exactly half-full.
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OK, my guess for the rope one. Something like burn one rope from each end, and start the other at one end. When the flames on the first rope meet, that's 30 minutes, which means the other rope has 30 minutes left. set fire to the other end ot the second rope, and when the flames meet that's half of 30 minutes, or 15 minutes, giving 45 minutes in total (not counting the time to set the rope on fire).
How'd I do?
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Sandrax and Rob are our winners! Congratulations :thumbsup:
And if you've got better puzzles, by all means please do post them :)
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PS This "brainteasers" are always fucking dumb because there're a million possible answers, but only one is the "correct one", and the only way you know that is if you heard it before. The best ones like this are the dead fisherman and the man that hangs himself.
aww have a heart
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aww have a heart
This is one that was posted at cprog when we had this thread.
There is a dead man by a river. He's in a phone booth, and there are holes in the side of the phone booth. How did he die?
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The holes were put in the phonebooth to tie the concrete blocks to it. He drowned.
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But it says that the man is dead by a river, not in one. The most obvious answer to me is that he was shot while talking in a phonebooth by a river, but that's not really in the spirit of these things.
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Since there is no fucking way anyone will possibly get this unless they've heard the "brain teaser" before, I'll just say the answer.
He was by the river because he was fishing. He caught a fish and went to call someone and tell them. When he did, he stuck his arms out to show how big the fish was, put them through the glass, and bled to death.
Man, you guys are sooooo dumb
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Here, Govtcheez, this one has a definite answer, and I know I figured it out without having heard it before.
An array A[1 . . . n - 1] contains all integers from 0 to n - 1, except one integer which is missing. Now suppose you cannot access an entire integer in A with a single operation, but you can access one bit of a number A at a time in O(1) time. Devise an algorithm to find the missing integer in O(n log n) time.
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See, that's different - that one I can't answer because I'm just not smart enough. I'm fine with puzzles like that :p
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See, that's different - that one I can't answer because I'm just not smart enough. I'm fine with puzzles like that :p
:lol: :lol: :lol: :lol: :lol: :lol: