A circuit is built from five 10 ohm resistors and a 12 V battery. One branch, call it the blue branch, has two of the 10 ohm resistors wired in parallel with each other, and that parallel pair is wired in series with a third 10 ohm resistor. What is the equivalent resistance of the blue branch alone?

1. First combine the two parallel resistors in the blue branch: 1/R_pair = 1/10 ohm + 1/10 ohm. 2. R_pair = 1 / (2/10 ohm) = 5 ohm. 3. This parallel pair is wired in series with the third 10 ohm resistor, so add the resistances: R_blue = R_pair + 10 ohm. 4. R_blue = 5 ohm + 10 ohm = 15 ohm. 5. 30 ohm would result from treating all three resistors as if they were simply added in series. _Source: OpenStax Physics (CC BY 4.0), Ch 19 "Electrical Circuits", section Strange-Looking Circuit Diagrams_