Continuing the same circuit: the blue branch (15 ohm) is wired in parallel with a red branch made of two 10 ohm resistors wired in series with each other (20 ohm). What is the equivalent resistance of the whole combination?

1. The blue branch resistance is 15 ohm and the red branch resistance is 20 ohm, and the two branches are wired in parallel with each other. 2. For two resistors in parallel: 1/R_equiv = 1/15 ohm + 1/20 ohm. 3. 1/15 ohm + 1/20 ohm = 4/60 ohm + 3/60 ohm = 7/60 per ohm. 4. R_equiv = 60/7 ohm, which is approximately 8.6 ohm. 5. 35 ohm would result from simply adding the two branch resistances together as if they were in series, not parallel. 6. about 17.5 ohm is exactly half of 35 ohm, an averaging shortcut that only works for two equal resistors, not these unequal branches. 7. about 12.0 ohm does not correspond to either the sum or the correct reciprocal-sum combination of 15 ohm and 20 ohm. _Source: OpenStax Physics (CC BY 4.0), Ch 19 "Electrical Circuits", section Strange-Looking Circuit Diagrams_