This problem seems pretty straightforward.. and yet I haven't made any significant progress at all.(adsbygoogle = window.adsbygoogle || []).push({});

"A parallel combination of an 7 resistor and an unknown resistor R is connected in series with a 12 resistor and a battery. This circuit is then disassembled and the three resistors are then connected in series with each other and the same battery. In both arrangements, the current through the 7 resistor is the same. What is the unknown resistance R?"

So I drew the circuit out, and I concluded that for the last statement to be true, the equivalent resistances must be the same (since every resistor in a series circuit feels the same current, by virtue of being in series.) So I wrote

[(1/7) + (1/R)]^-1 + 12 = 7 + 12 + R

Unfortunately this equation is woefully uninformative, as when it is simplified, it yields 1 = 1. Could I have a hint or two from the masters?

Thanks,

Stephen

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# Homework Help: Unknown resistance

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