A little and very easy brainbender « Thread Started on Dec 14, 2008, 1:30am »
Here's a little brainbender to think about-[don't worry it's far from as tough as the brainbenders on the MM site] You have two ropes . They aren't the same size, but if you light them at one end, they both burn for 60 minutes. They don't burn evenly all thoughout the 60 minutes- some parts of the ropes take longer to burn than others. You have a box of matches to light them with. Can you ,using only the two ropes and the matches, and a teeny bit of thinking, make BOTH ropes burn up in an excact time of forty-five minutes i.e. if you are watching the clockwhile the ropes are burning [though you don't have a clock in this simple brainbender] when both of the ropes are burnt up, forty-five minutes should have passed. Hint- you can light both ends at once.
Knowledge is important; but imagination is more so!
Joined: Mar 2006 Gender: Male Posts: 125 Location: Look behind you. Karma: 7
Re: A little and very easy brainbender « Reply #1 on Dec 19, 2008, 12:11pm »
The hint is too great a clue, and so is the number of ropes given.
Incidentally, I heard a similar problem with monks and incense sticks as opposed to ropes, and I was told that it was an interview question. Anyway:
burn one rope at both ends, the other at one end; when one is burnt up then 30 mins have passed - then burn the second (non-burnt) end of the second rope; obviously it will take (60-30)/2 = 15 mins for this second rope to burn up;
conclusion: once both ropes have been burnt, 30 + 15 mins have elapsed.
Re: A little and very easy brainbender « Reply #2 on Dec 20, 2008, 6:53am »
Yup, you got it right. I've entered the same riddle in the UMMF and they never answered it. Oh well, you can look at the thread- it's got a couple of other riddles that I entered- though the others have solved them already. You can still have a go at them, without looking at their replies, then check your answers
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