<PRE><B>Question 65167</B>
Given the formula 1/Rr = 1/R1 + 1/R2 + R3 for the resistance of a circuit, determine the resistance R3 if Rr = 3 3/7 ohms, R1 = 6 ohms, and R2 = 3 ohms. 
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Rr=3 3/7 = 24/7 then 1/Rr=7/24
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7/24 = 1/6 + 1/3 + R3
Multiply thru by 24 to get:
7 = 4 + 8 +24R3
24R3=-5
R3=-5/24
Cheers,
Stan H.
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