Maths puzzle

[EddieM]

Allegedly this is a question posed by Amazon in their interview for software engineers (why, I have no idea)

ok.

A 80m long cable is suspended from two 50m high poles. The centre of the cable is 10m above the ground.

To one decimal place (in metres) How far apart are the poles?

 

[rsgaz]

Spoiler

Zero?

 

[ellal]

Fairly obvious without resorting to maths!

 

[EddieM]

Fairly obvious without resorting to maths!

Well go on then?

 

[EddieM]

Spoiler

Zero?

No, neither is it the square root of SFA, or indeed 3 light years.

Haha Eddiem is officially WRONG!

 

[JohnD]

It's a question aimed at weeding out people who are used to the real world.

If you are familiar with cables and sags, you "know" that poles are not placed contiguously, so you might start thinking about chords and segments of circumference, since the accuracy required in the answer is so low that you don't need to calculate a parabola.

It is actually a riddle, not an engineering question, although the answer becomes apparent as soon as you start to draw, or visualise, the construction.

Amazon may or may not include riddles in their interviews. If they do, their victims need to be distrustful.

 

[EddieM]

It's a question aimed at weeding out people who are used to the real world.

If you are familiar with cables and sags, you "know" that poles are not placed contiguously, so you might start thinking about chords and segments of circumference, since the accuracy required in the answer is so low that you don't need to calculate a parabola.

It is actually a riddle, not an engineering question, although the answer becomes apparent as soon as you start to draw, or visualise, the construction.

Amazon may or may not include riddles in their interviews. If they do, their victims need to be distrustful.

Why is it a riddle it has a definitive calculable mathematical answer?

 

[JohnD]

As soon as you realise what the numbers imply, time and effort on calculation is wasted.

 

[EddieM]

As soon as you realise what the numbers imply, time and effort on calculation is wasted.

Huh?

 

[rsgaz]

No,

So, what's the answer then?

edit: Or is it some silly trick question because it doesn't say how high up the poles the cable is attached. They could be 80m apart if the cable was only attached 10 metres up each pole and was under incredible tension.

 

[EddieM]

So, what's the answer then?

edit: Or is it some silly trick question because it doesn't say how high up the poles the cable is attached. They could be 80m apart if the cable was only attached 10 metres up each pole and was under incredible tension.

Haha, I don't know! I'll try to find the video that explains it, WARNING it is really boring, so boring in fact I never got to the end of it.

 

[JohnD]

Huh?

Take an 80 foot cable. Attach both ends of it to the top of a 50 foot pole. Where is the lowest point of the hanging cable?

Or, to make it even easier, take a 40 foot cable and hang it from the top of a 50 foot pole. Same answer.

 

[EddieM]

 

[EddieM]

Tale a 80 foot cable. Attach both ends of it to the top of a 50 foot pole. Where is the lowest point of the hanging cable?

If the poles were as far apart as in the question posed then the answer would be 10 feet.

 

[JohnD]

Take an 80 foot cable. Attach both ends of it to the top of a 50 foot pole. Where is the lowest point of the hanging cable?

Or, to make it even easier, take a 40 foot cable and hang it from the top of a 50 foot pole. Same answer.

That's a single pole. Both ends attached to the same point. Zero distance between them.

Edit
I posted that before looking at your vid.