I'm pretty good at these things and I couldn't get this one myself.

A warden meets with 23 new prisoners when they arrive. He tells them, "You may meet today and plan a strategy. But after today, you will be in isolated cells and will have no communication with one another.

"In the prison is a switch room, which contains two light switches labeled A and B, each of which can be in either the 'On' or the 'Off' position. I am not telling you their present positions. The switches are not connected to anything.

"After today, from time to time whenever I feel so inclined, I will select one prisoner at random and escort him to the switch room. This prisoner will select one of the two switches and reverse its position. He must move one, but only one of the switches. He can't move both but he can't move none, either. Then he'll be led back to his cell.

"No one else will enter the switch room until I lead the next prisoner there, and he'll be instructed to do the same thing. I'm going to choose prisoners at random. I may choose the same guy three times in a row, or I may jump around and come back.

"But, given enough time, everyone will eventually visit the switch room as many times as everyone else. At any time anyone of you may declare to me, 'We have all visited the switch room.'

"If it is true, then you will all be set free. If it is false, and somebody has not yet visited the switch room, you will be fed to the alligators."


What is the correct strategy? If you already knew the answer don't post.

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“There's no sense in being precise when you don't even know what you're talking about.” - John von Neumann

Haha, this is gonna be fun... and very hard

have each person scratch a tally mark into the wall the first time they go in.... when 22 tallys are on the wall, the 23rd guy makes the declaration, and theyre free

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IIAv8tionII - ME
Av8tion - SCAMMER

Online Tournament Wins: 11

No, you can't use tallies/leave anything behind. There is actually a strategy involving only the switches.

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“There's no sense in being precise when you don't even know what you're talking about.” - John von Neumann

Hmm, I think it would take the prisoners a long time since it would require them to get a "scorekeeper" to see how many people have entered the "switch room"

theyre isolated.... they have NO CONTACT WHATSOEVER.... i thought of it too....

EDIT: never mind...you do need one.. i think i have it... a person going in for the first time makes sure a certain light is at a certain position... if a score keeper sees that light in a certain position, they add to their tally and hit that switch, once he's at 22 then it's good game... since there's only 4 permutations of lights, i guess this is the only way i see that it can be done..

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IIAv8tionII - ME
Av8tion - SCAMMER

Online Tournament Wins: 11

What if the certain position of the certain switch they use to tally is already in that position to begin with?

On the right track not really the correct answer.


On the right track still.

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“There's no sense in being precise when you don't even know what you're talking about.” - John von Neumann

the only way to keep track is through the 4 possible combinations of the 2 switches.
A up, B up
A up, B down
B up, A down
B down, A down

you need to select 2 positions as a "new" switch mover, and 2 as a "repeated" switch mover so I will use up up and A up B down as a new mover mark.

for instance If the 1st person finds both switches down he will move A up, therefor if he is led in again he will put A down and the next person will find them in the down down position. whatever the first configuration he can move it to a new mover position

otherwise a person will find them in the A up B down position and can then move to A up B up.

if he is led in again he puts them in the A down B up position letting the next person know the second person was in there twice, if it is a new person they put the switches to the A up B down positions, basically the 2 positions that cdesignate a new person are A up and B down and Both up, the other 2 positions mean there has been a repeat offender in the room.

when 1 person notices 22 seperate instances of A up B down or both up he knows they are free

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I find your response in this thread shallow, and pedantic...

HAHAHA, and you expect 23 people, let alone inmates figure this out, let alone remember and be able to follow it...

i know its a ridldle