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More ways to get Braingle...

Wood-cutting Machines

Logic puzzles require you to think. You will have to be logical in your reasoning.

 

Puzzle ID:#4820
Fun:*** (2.5)
Difficulty:*** (2.74)
Category:Logic
Submitted By:arij****

 

 

 



In a wood-cutting factory, four large sawing machines stand in a windowless room. Each machine has an on/off switch attached, there being no doubt as to which switch controls which machine. Outside the door to the room are four back-up on/off switches, one for each machine inside. The power for each machine must first pass through the back-up switch, and then the machine switch before reaching the saw. The problem is, the new manager cannot decide how these back-up switches match with the machines inside the room. One day, the manager's brother visits. The manager takes him inside the sawing room where all four machines are at work and explains the problem. The brother announces that he intends to leave the room and that when he returns he will be able to match correctly the four switches outside the room to the four machines inside. The brother works alone, cannot see the machines from outside the room and solves the problem purely by operating switches. How is it possible?




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Comments

na-iem
Mar 12, 2003

You gave me the impression that the machines cannot be "heard" outside the room when you said the machines cannot be "seen" from outside. What was the point of saying they cannot be seen from outside?
akshaysaxena
Jul 04, 2003

One alternative solution:
assumption: saw machines have wood fed in them.
go out. switch on first button for 5 seconds, second button for 10 seconds..third for 15 and fourth for 20 seconds.. no go inside and see how much wood has been cut by each of the saws, and thereby find out the correct switch connections.
LoonyAx
Jul 05, 2003

Another answer wood (pun intended) be to put all machine switches on, and go outside.

The first switch should not be touched at all.
The second one should be turned on for 20 minutes then turned off.
The third one should turned on for 20 minutes and left on.
The fourth one should be turned on right before he goes inside.

Now you can map them. How?

Well, the first switch's machine is off and cold.
The second one's is off and hot.
The third one's is on and hot.
The fourth one's is on and cold.

Ta-da!
taniapereira99Aca*
Jul 29, 2003

I also had the impression that nothing could be heard... or that the machines couldn't be checked
peanutAza*
Jun 23, 2005

Yeah, the logic's good but the whole 'can he hear or can't he' sould have been stated. GOOD answer LoonyAx, you're thinking like an Engineer - Nice one!
lessthanjake789*us*
Oct 11, 2006

ah, loony, i had the exact same answer, as this mimics the three light bulb question, i thought. clever and good.



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