(a) Calculate the total resistance of the circuit: (watch out for the bear trap)                                                             

1/Rtot = 1/30 + 1/40 + 1/50 = 0.0333 + 0.025 + 0.020  = 0.0783 W^-1

Rtot = 1/0.0783 = 12.8 ohms

(b) Work out the current through each resistor.                                                             

I = V/R Þ I1 = 12 ¸ 30 = 0.40 A ;

I2 = 12 ¸ 40 = 0.30 A ;  I3 = 12 ¸ 50 = 0.24 A

(c) Work out the total current                                                                                        

Itot = 0.40 + 0.30 + 0.24 = 0.94 A