I noticed that, for resistors in a parallel circuit, where R1 is < R2, the minimum value is (R1)/2, and the maximum approaches R1. I was trying to work out why, so for two resistors, the calculation is: R1.R2/(R1 + R2). I thought of partial derivatives but not sure where to go after that, and after getting the curve in WolframAlpha, not sure what to do with that either. http://www.wolframalpha.com/input/?i=plot+xy/(x+y) Empirically, the nth case appears to be: min = (R1)/n and max = R1, but not sure how to prove it mathematically. Any advice on what I could try next? This isn't homework, just noticed it and got curious.