>>< snip >
>>Assuming that we can ear the sound of the machines...
>>
>>Shut down 2 machines. (m1 and m2)
>>Go to the outside switchboard.
>>Shut down all switches.
>>Test every switch to determine (by the sound of the machine) the 2 on and the 2 off.
>>Switch on 1 running machine and 1 shut down machine.
>>Go inside the machine room.
>>Only one machine run, you know this machine map to which switch.
>>Now, test the two machines that was switch off before and you will know the second on switch mapping.
>>And its now easy to map the other 2 switches by deduction...
>>
>>:-)
>
>Let me compicate things just slightly by saying that once the brother leaves he can come back to the machine room only once. And once he has come back he must be able to determine which switches map to which machines.

Thats what I said...

Let me re-phrase:

IN THE ROOM
Brother shut down 2 machines. (Machine A and Machine B)

OUT OF THE ROOM
Brother play with the switches and by earing the sound was able to know the 2 switches that was assigned to the 2 running machines
and the 2 that was assigned to the stopped machines. Of course, he dont know to which of the 2 running machines the running switches map, same for the stopped machine. But he have now 2 pair of possibility.
Brother turn OFF the switch of one running machine switch and turn ON the switch of one of the stopped machine.

IN THE ROOM
One machine run, so Brother can say to which switch this machine was mapped (the one he left ON).
Now he know that the other that run when he first leave the room was mapped to the switch he turn OFF.
Brother try to start the machine C and D, the machine that start was mapped to the other ON switch and the other to the remaining OFF switch.


Thats all :-)