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23 Prisoners

Libre

Libre

Member
Here's an amazing brain teaser I heard some years back. I occupied my mind for a few days, before I gave up. I had a few solutions, but they didn't work anywhere as well as the real answer.
I thought it was compelling enough to write it up and post it on my site. Give it a try. There is a link to the solution if you want to give up - but think it over.
Like the best of these problems, it seems impossible, but the answer really does work.
I'd be interested in how you do, and if you thought this was thought provoking.

http://marcfriedlander.com/23_prisoners.htm
 
I took even less than that...I found it by clicking on the link at the bottom because, afterall, it's late in the afternoon and I'm all thought out. :(
 
I don't buy it. Many prisoners are quite stupid and wouldn't have remembered the rules. They'd fry.
 
Why do the prisoners need to move the right switch TWICE? Why not just do it once? Is that in case the switch is down at the very beginning and a prisoner flicks it before the Captain has started his count? In that case, wouldn't a count of 43 OR 44 work?
 
Kookamoor said:
Why do the prisoners need to move the right switch TWICE? Why not just do it once? Is that in case the switch is down at the very beginning and a prisoner flicks it before the Captain has started his count? In that case, wouldn't a count of 43 OR 44 work?
Click to expand...

Yeah - they don't know the initial position - it could be up or down. If it starts in the up position, then when the count reaches 44, everyone has been there twice except for 1 prisoner, who has only been there once. If it starts in the down position, when the count reaches 44, then everyone has been there twice. I'm going from memory here. These things confuse the hell out of me. Maybe Zolipara can explain it better. I'm not as clever as he is.
 
Kookamoor said:
Why do the prisoners need to move the right switch TWICE? Why not just do it once? Is that in case the switch is down at the very beginning and a prisoner flicks it before the Captain has started his count? In that case, wouldn't a count of 43 OR 44 work?
Click to expand...

Yes thats it. You need a count of 44 to make 100% sure everyone has been there.
 
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