1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Maths help two :)

Discussion in 'General Discussion' started by Orionaut, Apr 21, 2019.

  1. Orionaut

    Soldato

    Joined: Aug 2, 2012

    Posts: 6,522

    The other thread just reminded me of a question I saw many years ago (In New Scientist IIRC)

    Consider the situation...

    Imagine a string wrapped all the way around the Earths equator.

    Now imagine a second string raised to a point 1M above the earths equator.

    Q: How much longer is the second string than the first.

    I am not searching for the answer here, simply the method.

    What was your solution, and how did you arrive at it?

    ;) :p
     
  2. Jasoncmor

    Gangster

    Joined: Feb 13, 2010

    Posts: 415

    The second would be shorter, would it not?
     
  3. D3K

    Mobster

    Joined: Nov 13, 2014

    Posts: 2,880

    (2*pie*[r+1]) - (2*pie*r)

    Where r is the average radius of the earth in metres at the equator.

    But if you want to lay the string flat against every nook and cranny of the earth to get a true measurement, good luck :p
     
  4. Orionaut

    Soldato

    Joined: Aug 2, 2012

    Posts: 6,522


    Correct, but too complicated.

    There is a simpler way of looking at it ;):p

    Thats what I am looking for, not the solution but rather the logic.

    :)
     
  5. touch

    Capodecina

    Joined: Oct 28, 2006

    Posts: 11,073

    Location: Sufferlandria

    The equator doesn't have any altitude. There's no such thing as "1 metre above the equator"?
    Is it 1m above sea level at the equator or 1m above ground level? They're going to be very different things.
     
  6. Kenai

    Capodecina

    Joined: Apr 5, 2009

    Posts: 17,867

    It's a problem to demonstrate that to calculate the change in circumference of a circle as a result of change in diameter/radius doesn't require you to know the original circumference or diameter/radius.

    You're looking at it too literally if you're worrying about sea level vs ground level.
     
  7. D3K

    Mobster

    Joined: Nov 13, 2014

    Posts: 2,880

    You want me to factorise it?

    2*pie*(r+1/r)

    You need to know the radius to calculate the specific change. Even if you don't know it, radius/diam is still required in the equation.
     
  8. Kenai

    Capodecina

    Joined: Apr 5, 2009

    Posts: 17,867

    If you want to demonstrate working from first principle maybe but once you know that all the original figures drop out, it means you can happily calculate the change in one of those numbers simply by knowing the change in the other.
     
  9. Orionaut

    Soldato

    Joined: Aug 2, 2012

    Posts: 6,522


    All the information required is in the question. ;)
     
  10. D3K

    Mobster

    Joined: Nov 13, 2014

    Posts: 2,880

    Yeah ok fml it's 2 pie... meh
     
  11. Kenai

    Capodecina

    Joined: Apr 5, 2009

    Posts: 17,867

    I was trying to post in a way that didn't just kill the thread half a dozen posts in :p
     
  12. builder22

    Mobster

    Joined: Dec 14, 2005

    Posts: 2,519

    is this second string just hovering in mid air?

    are drones/helicopters/spaceship allowed to help???
     
  13. TNGL

    Wise Guy

    Joined: Jul 2, 2010

    Posts: 2,457

    Classic job interview brain teaser.
     
  14. Orionaut

    Soldato

    Joined: Aug 2, 2012

    Posts: 6,522


    True

    That was my logic when I first saw it. I haven't been told what the earths radius is, therefore it doesn't matter

    Once you accept that, the answer is clear.

    It is a bit like the "Monty hall" problem.

    People feel the need to come up with all sorts of complex arguments to explain how this, apparently, counter intuitive situation can arise.

    In fact it isn't complex at all.

    The solution is that it has little to do with probability and everything to do with the fact that the game show host knows which doors have the car and which have the Goat!
     
  15. builder22

    Mobster

    Joined: Dec 14, 2005

    Posts: 2,519

    btw, when you said 'raised to a point 1m above the equator' I thought you meant towards the North Pole, with the second string then being smaller, still wrapped round the earth....missed the fact you said the second string would be bigger!
     
  16. viathinair

    Wise Guy

    Joined: Nov 28, 2009

    Posts: 2,098

    Location: Englishman in the states.

    [​IMG]
     
  17. Pringle W

    Capodecina

    Joined: Oct 1, 2008

    Posts: 10,975

    Location: Glebe Park

    With all the winky faces by the op is the answer something humourous to do with eating pies?
     
  18. esmozz

    Gangster

    Joined: Oct 24, 2013

    Posts: 137

    The world is'nt a sphere.

    Google WGS84 and then work it out. Personnally I would have no idea.
     
  19. D3K

    Mobster

    Joined: Nov 13, 2014

    Posts: 2,880

    He isn't asking about spheres. He's asking about circumferences which are based on circles, and the equator is a circle.
     
  20. Nitefly

    Man of Honour

    Joined: Sep 24, 2005

    Posts: 30,991

    That’s what I thought so I’m intrigued as to what the super duper concise answer is.