Physics

I'm totally confused and this is due Monday-
We're dealing with electrical circuits and I have to construct a circuit with resistors of 10 Ohms, 20 Ohms, 30 Ohms and 20 Ohms. The total resistance has to be 42 Ohms-Can someone direct me how to even begin to draw this-I know Parallel resistors you add sum and take the reciprocal for total and series you had them together but where do I start with this-Please help_ I'm stuck and its the weekend and this is due Monday

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asked by Aubrey
  1. The 20 and 30 ohm resistors in parallel have an equivalent resistance of 12 ohms. Put the 10 and other 20 ohm resistors in series with that.

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    posted by drwls
  2. I drew my circuit but now I'm still confused-if I have a 20 V battery, how do I calculate the current through two of the resistors(say the two parallel ones of 20 and 30
    Would I use the formula
    V=IR
    20V =I*12Ohm(which I just figured out)
    20/12 = 1.67A But now I'm stuck because I don't know how to break it down into the 20 Ohm resistor and the 30 Ohm resistor

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    posted by Aubrey
  3. In my calculations I think I should have said V=IR
    V= 20V Battery I used so
    20V = I * 20 Ohm= 1A
    20V = I * 30 Ohm = .67A

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    posted by Aubrey
  4. Your original question just asked for how to arrange the resistors to achieve a total effective resistance of 42 ohms. I told you how to do that. The total current going through each series resistor, and the battery, will be V/R = 20/42 = 0.476 Amp

    The two resistors in parallel will share that current, with the lower (20 ohm) resistor getting 3/5 of it.

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    posted by drwls
  5. The reason I only asked the first part was I first wanted to understand how to construct it before I figured out the rest because I have three more sets of circuits to do so now I understand that part. I wasn't trying to mislead you-I really appreciate the help alot and can now continue with the other circuits using this as a basis-Thank you again for all your assistance

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    posted by Aubrey

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