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Homework Help: Finding distance of wire

  1. Oct 13, 2009 #1
    a copper wire 750ft long has resistance of 1.563. How long is a copper wire of the same cross-sectional area whose resistance is 2.605. Note: the resistance of these wire is proportional to their length.

    attempted to solve:

    then cross multiply
    750 * 2.605 = 1953.750/1.563
    = 1250 ft

    can someone advise if I am right

  2. jcsd
  3. Oct 14, 2009 #2


    Staff: Mentor

    You have set up the proportion correctly, but don't seem to understand what to do next.
    Your equation above has x in it. Where did it go?
    What you want to do is to get x all by itself on one side of the equation. When you do this, you will have solved the equation.

    Ignoring the units for the moment, you have 750/1.568 = x/2.605
    What operation can you do to both sides of this equation so that x is by itself? DO NOT SAY cross multiply.
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