Logical Interview Question

[LondonManc]

How do you propose to set fire to the rope?

Wrap it round your head, use a blowtorch. F**k the rules, it'd be worth it.

Either that or with the lighting device provided, given the inferences within the problem presented.

[OwlHoot]

If you light the rope from both ends it burns in half an hour, no matter how inconsistently it burns along its entire length.

Yes, I'd concede that is true if you can think of the rope as effectively "one dimensional" like a thin fuse wire, and that is probably how one is meant to consider it in the context of the problem.

But if the rope has a finite thickness then the combustion shooting down the fluffy fast-burning substance from one end could completely surround our supposed waxy slow-burning lump embedded within it entirely below the rope's surface before the combustion from the other end reaches it, and in that situation the two separate combustions become in effect one, or in other words the second is sort of nullified, and that was what I had in mind.

[OwlHoot]

But if the rope has a finite thickness then the combustion shooting down the fluffy fast-burning substance from one end could completely surround our supposed waxy slow-burning lump embedded within it entirely below the rope's surface before the combustion from the other end reaches it ...

Hmm, thinking about it some more, there's no way combustion zones from opposite ends can "overlap" at any stage, assuming nothing is left after combustion. Also the zone from a given end must be in one part i.e. simply connected rather than multiple "islands".

So even for a "3d" rope, when both ends are lit one can think of the entire rope volume as comprising two disjoint simply-connected combustion regions, however irregular and intertwined these may be.

(So LondonManc & WFH are correct )

[BigRed]

Yes, I'd concede that is true if you can think of the rope as effectively "one dimensional" like a thin fuse wire, and that is probably how one is meant to consider it in the context of the problem.

But if the rope has a finite thickness then the combustion shooting down the fluffy fast-burning substance from one end could completely surround our supposed waxy slow-burning lump embedded within it entirely below the rope's surface before the combustion from the other end reaches it, and in that situation the two separate combustions become in effect one, or in other words the second is sort of nullified, and that was what I had in mind.

Well done sir! a fine defense of an increasingly tenuous position. Never surrender, never admit you were wrong. All that is lacking is your sockie explaining how it's obvious that's what you meant and the rest of us are a bunch of boneheads.

[LondonManc]

Hmm, thinking about it some more, there's no way combustion zones from opposite ends can "overlap" at any stage, assuming nothing is left after combustion. Also the zone from a given end must be in one part i.e. simply connected rather than multiple "islands".

So even for a "3d" rope, when both ends are lit one can think of the entire rope volume as comprising two disjoint simply-connected combustion regions, however irregular and intertwined these may be.

(So LondonManc & WFH are correct )

You've not got the gig because you sent the interviewer to sleep. HTHBIDI

[OwlHoot]

You've not got the gig because you sent the interviewer to sleep. HTHBIDI

If a question about burning ropes does come up in an interview, I'll walk it now!

[LondonManc]

If a question about burning ropes does come up in an interview, I'll walk it now!

[Dactylion]

If a question about burning ropes does come up in an interview, I'll walk it now!

If a question about burning ropes does come up in an interview, I'll walk out now!

[SueEllen]

If a question about burning ropes does come up in an interview, I'll walk out now!

Answer it and ask them to solve something else. When they protest tell them stupid irrelevant interview questions can be asked by both parties.

[scooterscot]

Cut or mark each rope into four equal lengths. Remove the last quarter of each piece or set.

Ignite each set. The period of time between the piece that remains lit and the other extinguished equals 45 minutes.

I'd argue this answer is more accurate than that given since you're only igniting the rope once.