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Homework Help: Parallel and Series Resistor Simplification

  1. Apr 13, 2009 #1


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    I need help simplifying this circuit with parallel and series resistors. I am mainly confused, because there seems to be a point in my simplification where in picture 4 and 5 of my second image where the remaining 3 resistors are connected by 1 node.

    I tried to simplify them as resistors in parallel, but I end up with the wrong answer, and this doesn't seem like the correct thing to do.

    1. The problem statement, all variables and given/known data

    The Resistor equivalent of the entire circuit is 9 ohms. And the answer for 'R' is 15 ohms. However I do not know how to obtain this answer.

    2. Relevant equations

    Series Resistors = R1 + R2 = Rtotal
    Parallel = R2*R1/R1+R2 = Rtotal
    = 1/R3 + 1/R2 + 1/R1 = Rtotal

    3. The attempt at a solution

    Here are the images of my attempted solutions:

    image 1 (the problem):
    http://img22.imageshack.us/img22/9206/resistor1.jpg [Broken]

    image 2 (my analysis):
    http://img22.imageshack.us/img22/4978/resistor2.jpg [Broken]

    Any help would be appreciated.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 15, 2009 #2
    the 30ohm resistor is shorted so just remove it from the network and u'll get the right answer.
  4. Apr 15, 2009 #3


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    Yes, thank you.

    I actually figured it out before the forum posted my question.
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