Question

what is the highest and lowest total resistance that can be required by the combinations of 4 coil of resistance 4 ohm 8 ohm 12 ohm 24 Ohm

Answer 1

max resistance will be when these are arranged in series ...

Rmax = 4+8+12+24 = 48 ohm

mini resistance will be when these are arranged in parallel ...
Rmin = 2 ohm

$\frac{1}{r} = \frac{1}{4} + \frac{1 }{8} + \frac{1}{12} + \frac{1}{24} = \frac{12}{24} = \frac{1}{2}$