What is the (a) highest (b) lowest total resistance, that can be secured by combinations of four coils of resistances 4 ohms, 8 ohms, 12 ohms and 24 ohms?
Highest will be by series = 4+12+8+24=48 ohms
Lowest will be by parallel =1R=14+18+124+112=1224=12
so R = 2