(a) What is 100 mA in amps?                                                                                           (1)

100 mA = 0.1 A

(b) What is the current in each resistor?                                                                           (1)

0.1 A 

(c) Work out the voltage across each resistor.                                                                  (3)

V = IR Þ V1 = 0.1 ´ 30 = 3 V ; V2 = 0.1 ´ 40 =  4 V ;

V3 = 0.1 ´ 50 = 5V

(d) What is the total resistance?                                                                                       (1)

Rtot = 30 + 40 + 50 = 120 ohms

(e) What is the battery voltage?                                                                                       (1)

V = 0.1 ´ 120 = 12 volts