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In an electric circuit, two resistors with resistances \(x\) and \(y\) are connected in parallel. In this case, if \(r\) is the combined resistance of these two resistors, then the reciprocal of \(r\) is equal to the sum of the reciprocals of \(x\) and \(y.\) What is \(r\) in terms of \(x\) and \(y?\)
(A) \(xy\)
(B) \(x + y\)
(C) \(\dfrac1{x + y}\)
(D) \(\dfrac{xy}{x + y}\)
(E) \(\dfrac{x + y}{xy}\)
Answer: D
Source: Official Guide
(A) \(xy\)
(B) \(x + y\)
(C) \(\dfrac1{x + y}\)
(D) \(\dfrac{xy}{x + y}\)
(E) \(\dfrac{x + y}{xy}\)
Answer: D
Source: Official Guide
