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    Paper is wrapped round a cardboard cylinder exactly 3 times.
    The cylinder is 70 centimetres long.
    The area of the paper is 3000 square centimetres.
    Calculate the diameter of the cylinder.




    I am sorry. I could not copy and paste the picture. But it basically looked like kitchen roll on its side. I have no idea how to calculate the diameter of the cardboard cylinder that the paper is wrapped around. Please help.
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    Surface area of this particular cylinder:  A = \pi .d.h

    From the question, the height is 70cm.
    surface area = 3000/3 = 1000cm^2 (we know this because the paper wraps round the outside 3 times, and the paper is 3000cm^2)

    d is the diameter, so shove this all into your equation and you get:
     1000 = 70\pi. d
    d = \frac{1000}{70\pi }

    Plug that into your calculator and there's your answer! If you don't understand how I got anything, just say and I'll explain
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    (Original post by Hype en Ecosse)
    Surface area of this particular cylinder:  A = \pi .d.h

    From the question, the height is 70cm.
    surface area = 3000/3 = 1000cm^2 (we know this because the paper wraps round the outside 3 times, and the paper is 3000cm^2)

    d is the diameter, so shove this all into your equation and you get:
     1000 = 70\pi. d
    d = \frac{1000}{70\pi }

    Plug that into your calculator and there's your answer! If you don't understand how I got anything, just say and I'll explain
    Ahh thank you, i understand all of that now, that has been a really big help, you have no idea !
 
 
 
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Updated: September 26, 2011

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