Find R_{AB}. A 25 Ω resistor goes from A to node P. From P, a 30 Ω resistor goes to node R and a 10 Ω resistor to a middle node M. M connects to R through 20 Ω and to the bottom wire B through 5 Ω. R connects to B through 15 Ω. (Hint: convert the star 10–20–5 Ω at M into a delta.) (answer in Ω)