The circuit power supply is a constant current source of 10 Amps when there is a load across it. Close one switch there is 10 Amps thru a 10 Ohm resistor which is 100 V. Close two switches the 10 Amps splits you got 5 amps thru each 10 Ohm resistor which is 50 Volts. Close all three switches the 10 amps split you got 3.33 Amps thru each 10 Ohm resistor which is 33.3 Volts.
