Three resistors of value 2r, 3r and 5r are connected in series with each other. The voltage source applied to this combination is 20 V. If the lowest resistance is 4 Ohms, what is value of current flowing through the circuit?

1 A

R_eff = 2r + 3r + 5r = 10r

lowest resistance = 2r = 4 Ohms

Thus, r = 2 Ohms

R_eff = 10r = 10 (2 Ohms) = 20 Ohms

I = V/R_eff = 20 V/20 Ohms = 1 A