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Logic problem

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seti44
Posts: 52 - Karma: 32
so this is a logic problem from an interview. pretty cool answer once you think about it:

So you have two blocks that are non-uniform density and all you know is they are flammable and that they each take an hour to burn. How do you measure 45 min? (non-uniform density means that when it is half way burnt it does not necessarily mean that 30 minutes have passed)
Feb 8 2012 1:16AM
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JakeAssBeatClap
Posts: 6673 - Karma: 2,535
Glance at your watch/phone/clock on the wall when you start burning them and then wait until 45 minutes have passed.
Feb 8 2012 1:17AM
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Raz.
Posts: 7456 - Karma: 1,611
you measure 45 minutes with a stop watch. the other info had absolutely nothing to do with the question.
Feb 8 2012 1:19AM
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.AR6rider.
Posts: 15976 - Karma: 8,799
Light one block on fire from both ends, and one block at only one end, and we can assume that the block burning at both ends will burn in 30 minutes. After block A is completely burned out, we can assume that 30 minutes have passed, and light the other end of block B. Assuming it burns the same way as block A, and lighting the block at both ends will reduce the time it takes to burn by half, we can assume that the rest of block B will burn up in 15 minutes of the 30 remaining, equaling 45 minutes total. BOOM, headshot.
Feb 8 2012 1:21AM
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Skiing.Nz
Posts: 279 - Karma: 49
Count every second. Only logical way to do it.
Feb 8 2012 1:22AM
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seti44
Posts: 52 - Karma: 32
haha i feel like this might be slightly plagarized, but you could just be a well spoken individual. Nonetheless you sir win karma.
Feb 8 2012 1:23AM
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Skiing.Nz
Posts: 279 - Karma: 49
Wow.. that was impressive nice job sir.
Feb 8 2012 1:24AM
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MACAQUE
Posts: 2811 - Karma: 696
That makes absolutely no sense. You're assuming that the flame will not meet until the entire block is consumed. Lighting 2 fires on the same block doesn't mean it will burn faster according to the restrictions given in the problem.
Feb 8 2012 1:25AM
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.AR6rider.
Posts: 15976 - Karma: 8,799
To be honest, I've never heard of this logic puzzle being used with a block. My physics teacher in high school used to be obsessed with stuff like this, and when he asked us it was with a rope, so it makes more sense to burn it at both ends haha. I already knew the answer, just substituted block instead of rope.


Sorry for cheating, guys.
Feb 8 2012 1:30AM
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MACAQUE
Posts: 2811 - Karma: 696
Yea that would make more sense but I think the problem is still too vague. You'd need details like if the burn rate was limited by the amount of oxygen etc.
Feb 8 2012 1:35AM
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seti44
Posts: 52 - Karma: 32
haha yeah that's just how my friend relayed the question to me. It does make more sense to ask it using ropes instead of blocks though.
Feb 8 2012 1:36AM
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