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Math Help - help please with this problem

  1. #1
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    Post help please with this problem

    a cylindrical concrete pipe is to be cast so that the concrete is uniformally 75mm thick while the cross section of the concrete is 0.164m squared. formulate and solve the simultaneous equations showing the relationship between the external radius, R, and the internal radius r, of the pipe
    many thanks
    jim
    Last edited by jim49990; January 22nd 2007 at 11:55 AM. Reason: sorry wrong place to post
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  2. #2
    MHF Contributor
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    Quote Originally Posted by jim49990 View Post
    a cylindrical concrete pipe is to be cast so that the concrete is uniformally 75mm thick while the cross section of the concrete is 0.164m squared. formulate and solve the simultaneous equations showing the relationship between the external radius, R, and the internal radius r, of the pipe
    many thanks
    jim
    Let R = external radius
    And r = internal radius

    Given:
    R -r = 75mm = 0.075 m -----------(1)

    pi(R^2 -r^2) = 0.164 sq.m. -------(2)

    So,
    pi[(R+r)(R-r)] = 0.164
    pi[(R+r)(0.075)] = 0.164
    R+r = 0.164 / 0.075pi
    R +r = 0.696 m ---------------------(3)

    (1) plus (3),
    2R = 0.075 +0.696 = 0.771
    R = 0.771 /2 = 0.3855 m -----------***

    (3) minus (1),
    2r = 0.696 -0.075 = 0.621
    r = 0.621 /2 = 0.3105 m ------------***
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