As a design engineer, you are asked to design a lighting system consisting of a 70-W power supply and two lightbulbs as shown in Fig. 2.124. You must select the two bulbs from the following three available bulbs.
R1 = 80Ω, cost = $0.60 (standard size)
R2 = 90Ω, cost = $0.90 (standard size)
R3 = 100 Ω, cost = $0.75 (nonstandard size)
The system should be designed for minimum cost such that I = 1.2 A ± 5 percent?