Q. Suppose you have three resistors of 20 ohm , 50 ohm and 100 ohm . What minimum and maximum resistances can you obtain from these resistors?

(a) 15Ω , 170Ω

(b) 12.5Ω , 170Ω

(c) 12.5Ω , 150Ω

(d) 15Ω, 150Ω

Ans: (b)

For minimum resistance , all the resistors are connected in parallel.

$ \displaystyle \frac{1}{R_{min}} = \frac{1}{20} + \frac{1}{50} + \frac{1}{100} $

For maximum Resistance , all the resistors are connected in series

R_{max} = 20 + 50 + 100 = 170 ohm