If two resistors of 25 Ω and 15 Ω are joined together in series and then placed in parallel with a 40 Ω resistor, the effective resistance of the combination is: a) 0.1 Ω b) 10 Ω c) 20 Ω d) 40 Ω

The correct option is c) 20 Ω

The resultant resistance obtained from the resistors that are placed in series combination is connected with 40 Ω in parallel such that the overall resistance obtained is equal to 20 Ω.