From the datasheet, max ratings: Ib = 60pA Ios = 30pA Vos = 30mV Although the solutions list the datasheet offset as the answer (30mV), it considers the bias current quickly to see how much of an effect it has, and I am confused by the method. Essentially the calculation is Ios_(450k||50k) = Voff Which is equal to 2.7uV (negligible) I do not see how that circuit equation was obtained. It also says Ios+ is "absorbed" by Vin, which I don't understand either. What I got was: Vout/450k + Ios_ = 0, solving for Vout = -27uV I treated the node between the 50k and 450k as virtual ground, thus rendering the 50k irrelevant, which I'm guessing is incorrect, but I don't know how to proceed. I simply did superposition, considering the effect of each non-ideality separately, thus turning the rest off.