NDS Interview Question: puzzle 2:this is difficult on... | Glassdoor

## Interview Question

Software Engineer Interview Bengaluru (India)

# puzzle 2:this is difficult one.There are 2 ropes which u

can fire up and it'll burn.Each rope will take 1 Hour to burn completely.But this doesn't mean in half-an-hour half of the rope will be burnt.Burning process is uneven.How can u predict WHAT IS 15 MIN in the terms of rope????

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Answer: You light three ends at the same time, or as close to the same time as you possibly can. So you light two ends of one fuse and one end of the other fuse.

When the first fuse, the one whose both ends are lit, has completely burned up, that's half an hour. Because if it took an hour for it to burn from A to B, one end to the other end if you light both ends the whole fuse will be consumed in half an hour.

In the meantime that other fuse has been burning. If, as soon as the first fuse has burned up completely, you light the last end. So you've used up half an hour, and now it takes another 15 minutes for the new end to catch up to the original lit end and voila!

Interview Candidate on May 21, 2012
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Suppose the interviewer comes back with: &quot;Well, we tried that procedure, and it actually measured close to 16 minutes, not 15. How is that possible?&quot;

Nick on Jun 7, 2012
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@Interview Candidate: From the question -&gt; &quot;this doesn't mean in half-an-hour half of the rope will be burnt.Burning process is uneven&quot; - so that answer won't fly.

Whoa on Oct 30, 2015