Help desperate for riddle/brainteaser answer!

[cephyn]

Driving me mad. Can't find answer. Stumped. help!



100 prisoners in solitary cells. There's a central living room with one light bulb; the bulb is initially off. Everyday, the warden picks a prisoner at random, and that prisoner goes to the central living room. While there, the prisoner can toggle the bulb if he or she wishes. Also, the prisoner has the option of asserting the claim that all 100 prisoners have been to the living room. If this assertion is false (that is, some prisoners still haven't been to the living room), all 100 prisoners will be shot for their stupidity. However, if it is indeed true, all prisoners are set free and inducted into MENSA, since the world can always use more smart people. Thus, the assertion should only be made if the prisoner is 100% certain of its validity. The prisoners are allowed to get together one night, to discuss a plan. What plan should they agree on, so that eventually, someone will make a correct assertion?

 

[kmad]

Kill them all

 

[ainwood]

From a probability point of view, it will take an estimated (approx) 518 days before everyone has been picked.

The estimated lif of a bulb is about this time, so simply instruct everyone tp leave the light on. When the bulb blows, then this will indicate that the required length of time has passed, so put the assertion then.



(OK there's some dodgy logic here but...... )

 

[Becka]

The only thing I could think of is that they decide to leave the light on if they've been there, since the warden probably wouldn't just bring two inmates in, but would either bring in one or all one hundred.

 

[insurgent]

Could they not all turn on and off the bulb just the first time they enter the room. And when the bulb has been turned on and off 100 times, they know 100 prisoners have been in the room? But then, they may not be able to see the whether the bulb is turned on from their cells, probably not.

I assume that the prisoner leaves the room again after visiting it. If not, then they can all just wait until all 100 prisoners are in the room...

 

[Jason Fox]

Is this definitely the entire puzzle? You didn't leave anything out? Having trouble figuring how it could be cumulative and definitive for all prisoners.

Where did you hear this? Please respond as it's driving me and my coworker crazy now too, thanks.

 

[Flatlander Fox]

If they all get together everynight to discuss a plan, why not ask who has been there, and who hasn't?

 

[Jason Fox]

Originally posted by Flatlander Fox
If they all get together everynight to discuss a plan, why not ask who has been there, and who hasn't?

I think they only get together once, before the first one goes. The rest of the time they are either alone in their cells with no view of the room or alone in the room but they can't communicate except by leaving the light on or off.

 

[cephyn]

Thats the riddle, verbatim. I didn't leave anything out unless i copy/pasted wrong. Its from http://www.ocf.berkeley.edu/~wwu/riddles/intro.shtml

Site seems slow today, but thats where i got it.

 

[amadeus]

You'd ask all 100 prisoners if they have seen the light?

 

[Jason Fox]

Originally posted by rmsharpe
You'd ask all 100 prisoners if they have seen the light?

Assume you are a prisoner. You can't talk to any of the other prisoners (in isolation) and have no way of knowing who has been there and who hasn't, unless you work out a system with the light switch, which is the problem.

 

[amadeus]

But the prisoners get to meet once to work out a plan.

 

[Jason Fox]

They meet once but before they start getting selected to go into the room. It's so they can make a plan to be sure they declare they've all been there after they all actually had.

 

[Lefty Scaevola]

I have seen a varient of this before, with five persons. That may indicate that the solution is not dependant on the exact number of people.

 

[drake]

Head criminal dude:

"Listen boys, we ain't going anywhere anytime soon, seeing how we're in solitary confinement, so lets let patience rule this game. We wait 5 years (2125 days), and whoever gets picked to go in 5 years from now says that you're sure we've all visited due to the law of averages or some ****. The chances that someone has not visited in this amount of time is so slim, its worth the risk. Trying to think of any other way makes my brain hurt and besides since we're all criminals who got caught, even if we did come up with a plan, one of you morons is bound to screw it up anyway."

 

[Globber]

lol.... but I'd probably work... better yet, wait for some liberal yuppies to start complaining about conditions in prison because they have nothing better to do and get them all released...

 

[chiefpaco]

It never says explicitly they have to get together before the picking starts. But it does kinda say maybe they do by using the word, "eventually".

 

[cephyn]

yer right chiefpaco, but lets say they get together after 50 days, and only 35 guys have been in the room -- you still have the same problem, only with 65 prisoners instead of 100. So its best to assume that you meet the night before the first day, to come up with a good plan.

I still havent figured it out. 8(

 

[Magnus]

Each agrees to only change the light bulb's status upon their first visit there, every subsequent time they go there again they do not change it, therefore it will be 'changed' exactly 100 times and when the 100th dude finally gets chosen, he will have counted 99 changes beforehand.

 

[VanillaCube]

Originally posted by Magnus
Each agrees to only change the light bulb's status upon their first visit there, every subsequent time they go there again they do not change it, therefore it will be 'changed' exactly 100 times and when the 100th dude finally gets chosen, he will have counted 99 changes beforehand.

??????
say your the 98th guy in there. how do you know how many changes were made beforehand?


can all 100 of them meet IN the living room to discuss the plan? cause if they could they should meet in there and then all 100 would have visited the place. It didn't say WERE they would meet.


I think the real question is why are we trying so hard to get an anwser to let 100 criminals go free?