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What is the value of the third resistor?

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  1. samfulton is offline Junior Member Pro Subscriber
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    What is the value of the third resistor?

    A three-branch parallel circuit has a total resistance of 385.83 ohms. Two of the resistors are 680 ohms and 1500 ohms. What is the value of the third resistor?
    Your Answer: 2180 ohms
    Why is this wrong

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  3. kwegley is offline Junior Member Pro Subscriber
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    Quote Originally Posted by samfulton View Post
    A three-branch parallel circuit has a total resistance of 385.83 ohms. Two of the resistors are 680 ohms and 1500 ohms. What is the value of the third resistor?
    Your Answer: 2180 ohms
    Why is this wrong
    Let x = third resistor
    1/R1 + 1/R2 + 1/R3 = 1/Rtotal
    Rearrange the equation
    1/Rtotal - 1/R1 - 1/R2 = 1/R3
    1/358.83 - 1/680 - 1/1500 = 1/x
    When solved x = 2200 ohm

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  5. cbmcbride is offline Junior Member Pro Subscriber
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    Quote Originally Posted by kwegley View Post
    Let x = third resistor
    1/R1 + 1/R2 + 1/R3 = 1/Rtotal
    Rearrange the equation
    1/Rtotal - 1/R1 - 1/R2 = 1/R3
    1/358.83 - 1/680 - 1/1500 = 1/x
    When solved x = 2200 ohm
    I believe this is incorrect, can you actually demonstrate your calculations!

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