1. The problem statement, all variables and given/known data The overall resistance of the circuit is 12.5Ω. Calculate the value of the resistor labelled R in the circuit. 2. Relevant equations 1/R = 1/R1 + 1/R2 R = V/I 3. The attempt at a solution I understand that you use the first equation for parallel resistors and the second to calculate resistance from voltage and current. The bit I am having trouble with is the network of 4 resistors on the left hand side. The resistance on the right hand-side is 1/R = 1/2 + 1/6, so R = 1.5. So then 12.5 = 6 + 1.5 + the resistance of the left hand-side network. I just need guidance on how to calculate it because it puzzles me as there is 2 resistors between the other 2 in parallel.