by pebe » Thu Apr 23, 2015 4:32 pm
I make the answer 8.57V across the resistor.
Using Thevenin, R1 and R4 in the circuit can be replaced by the equivalent of the two resistors in parallel, and fed from the open circuit voltage at their junction. So we have 3.2ohms fed from 20 x 4 / 20 = 4V. Similarly, R2 and R3 can also be replaced by a single resistor of 3.2ohms and fed from 20 x 16 / 20 = 16V.
So in effect we have R3 (16ohms) in series with 2 x 3.2V with 12V across them. So the voltage across R3 = 12 x 16 / 22.4 = 8.57V, ie. 14.285 V at one end and 5.715V at the other.