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Author Topic: The questions, riddles and puzzles thread  (Read 37925 times)

Strife26

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Re: The questions, riddles and puzzles thread
« Reply #255 on: March 17, 2011, 02:20:01 am »

A number isn't always a number. Sometimes it's a couple of numbers next to each other.
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ed boy

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Re: The questions, riddles and puzzles thread
« Reply #256 on: March 18, 2011, 01:27:33 pm »

Here's one for you:

There an infinitely long train line, with a station every mile. Somewhere on this train line is a train. You are told the following:
-The train's speed is constant
-The train initially starts at one of the stations
-One hour later, the train passes through another station

You are tasked with finding this train. You are given a magical telephone that allows you, once an hour, to phone up a station and ask the station manager if the train is currently there. You are also, for the purposes of this exercise, immmortal, so you will be able to do a lot of phoning the stations.

How will you use the above to find a method for predicting which stations the train will visit, and when?
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Heliman

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Re: The questions, riddles and puzzles thread
« Reply #257 on: March 18, 2011, 01:54:57 pm »

Call the first station and ask how long ago the train left, and the # of hours equals the # of the station the train is at?

or failing that, Call a random train station, ask if the train was there before, and if not keep calling that train station every hour until it does.
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Criptfeind

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Re: The questions, riddles and puzzles thread
« Reply #258 on: March 18, 2011, 01:59:13 pm »

I think you can only ask if the train is there.
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rarborman

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Re: The questions, riddles and puzzles thread
« Reply #259 on: March 18, 2011, 02:19:38 pm »

Ask for the train's callsign, ask the callsign name station which way the train went, call station that it should be at time to direction.

Trains are very predictable.
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Ampersand

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Re: The questions, riddles and puzzles thread
« Reply #260 on: March 18, 2011, 02:23:06 pm »

I think you can only ask if the train is there.

In any case, I think I can come up with a good solution provided there is a way of knowing which direction the train was headed, but with so little information known about the train, the best you can do at this point is to call stations at random forever.
« Last Edit: March 18, 2011, 02:32:36 pm by Ampersand »
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Sowelu

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Re: The questions, riddles and puzzles thread
« Reply #261 on: March 18, 2011, 02:44:34 pm »

Train's speed is constant...So it doesn't slow or stop.

Well, look at the length of a train plus the length of a station; it's significant (if not necessarily large) compared to a mile.  So you've got that going for you.

My guess is that if you continually call stations at random, your probability of eventually catching the train, somewhere, within infinite time, isT+S where T is the length of the train in miles and S is the length of the station in miles.  Chances might be good that you never actually find it.  I'm sure I should probably be expressing this in sigmas or limits or something better like that but I don't know.
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ed boy

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Re: The questions, riddles and puzzles thread
« Reply #262 on: March 18, 2011, 05:55:28 pm »

You do not know which station the train starts at, or the one that it passes through at 1 hour.
You are only told if the train is at the station currently or not - you cannot ask if it has previously been at the statement.

There is a way to do it, and it is not guessing randomly.
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Darvi

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Re: The questions, riddles and puzzles thread
« Reply #263 on: March 18, 2011, 05:56:43 pm »

My solution -> Stop caring about that crap and start abusing your immortality to do something fun.
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Criptfeind

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Re: The questions, riddles and puzzles thread
« Reply #264 on: March 18, 2011, 05:59:26 pm »

Immortality does not sound that fun. What are you going to do? Take a long term position on stocks?
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Darvi

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Re: The questions, riddles and puzzles thread
« Reply #265 on: March 18, 2011, 06:25:37 pm »

No, I mean stuff like jumping of a cliff into jagged rocks or something. At least it's more fun that trying to waste an infinite amount of time on traintracking.
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ed boy

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Re: The questions, riddles and puzzles thread
« Reply #266 on: March 18, 2011, 06:48:24 pm »

My solution -> Stop caring about that crap and start abusing your immortality to do something fun.
As it so happens, you can think of nothing more fun than to hunt down this train. Oh, what a blast it will be.
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irmo

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Re: The questions, riddles and puzzles thread
« Reply #267 on: March 18, 2011, 08:27:35 pm »

How will you use the above to find a method for predicting which stations the train will visit, and when?
Spoiler (click to show/hide)
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ed boy

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Re: The questions, riddles and puzzles thread
« Reply #268 on: March 18, 2011, 09:34:46 pm »

How will you use the above to find a method for predicting which stations the train will visit, and when?
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irmo

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Re: The questions, riddles and puzzles thread
« Reply #269 on: March 19, 2011, 02:39:51 am »

Spoiler (click to show/hide)
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