I'm working on his problem and I know the answer and how it is derived. There is an older thread on this specific problem; however, I do not understand why the answer was derived in such a fashion. My approach to the problem using nodal analysis was to add the three currents stemming from the top node and set them equal to zero. I set the node where all three resistors meet to be the reference node. Substituting the currents with voltages and resistance yielded: (30V/2kΩ) + (20V/5kΩ) + (Vo/4kΩ) = 0 The correct answer is derived from the following equation: ((30V-Vo)/2kΩ) + ((20V-Vo)/5kΩ) + (Vo/4kΩ) = 0 I don't understand why Vo is supposed to be subtracted from each of the voltage sources when it is not between the path from the non-reference node to the node. I find I have problems similar to this in many circuit problems. I do well in subjects from understanding why things work the way that they do, and it seems that in this subject I seldom understand what assumptions can be made or why. Any help is greatly appreciated!