"Taiwan" is fine, Bodhidharma (unless you ask China...). Nonetheless, you are quite welcome indeed. It's my pleasure to share them.

Xie xie nin, Interrobang ( since you are in Chinese Taipei ) for the wonderful puzzles....

And Kevin, stop reminding me of food....I have been stuffing myself silly for the past 3 days !

hahaha. reminds me what my math teacher in high school used to say everytime i walked into the room " i smell bacon burnin" good old mr newberry.

mmm..especially when it's loaded with enough fat to sizzle !!! One reason why I love Hungry Jacks !

mmmmmm bbq

No, 3 go for burgers and leave Kevin to burn like a burger on the electric chair !!!

You got it! One prisoner (let's call him Kevin) has the job of counting the number of times he finds the switch flipped on. If he sees it on, he turns it off; otherwise, he ignores it.

The other three prisoners' only job that the first time they see the swith off, they flip it on. If it's on or if they've already flipped it once, they leave it alone. So each of them will only flip the switch once, and only from off to on.

Kevin waits until he has seen the switch on (and flipped it back off) three times, and then he delivers the news to the warden, and then all four prisoners go out for burgers.

chess players are inherently cautious !

once is enough. dont want to be there that long

Alright, alright...this is how we'll do it. We nominate Kevin as the class president...only he can turn the switch off. BTW, only he can make any assertion....others just keep quiet ! All the others can only turn the switch on. And they are turn it on twice - in other words, they must have had two visits ( Kevin wants to be doubly sure...but being paranoid, he prefers 3 visits but the other blokes are just itching to get away from prison, so 2 is quite enough ).

If Kevin was the first to go in, he sees the switch off, he leaves it alone. If he sees it on, he switches it off. Being a smart chap, he knows that there is already one prisoner in the room..."why ! It is I" he exclaims. When other prisoners have their turn, they turn the switch on if it is off. If it is off, they are to leave it alone.

So if Kevin counts that the number of times the switch was on ( in this case 6 ) after he switch it off ( this is possible only when Kevin is selected to visit the room )...by the way, this may still take 30 years to happen when the sadistic warden plays the dirty trick on them and "randomly" select the same chap to go into the room for 29 years, then he would know that every prisoner has been into the room. Meanwhile execution by electric chair has to be moved to another prison since all this fooling around with the switches is distorting electricity supply...and also no condemned man wants to disturb the wonderful game by asking for electrocution at this prison.

I'll tell tomorrow unless anyone else still wants to try.

whats the answer?

Bodhidharma, your idea doesn't work in the case that one of the prisoners never gets selected within the amount of time the designated one is willing to wait. It doesn't matter what Kevin says - since the selection is random, there's a chance that they'll die if they follow your plan (diminishing over time, but still more than zero), so it's not the solution.

There is a real solution, if anyone else cares.

No Interrobang...Kevin246 says that it works...and that's all it counts !!!

After a reasonably long time, the probability that everyone's been is too great. Hip Hooray !!!

Sorry Bodhidharma. You're close, but the one prisoner who makes the assertion in your strategy has no way of knowing that all of the other prisoners have been there. Even if he waits a hundred years, there's a chance he'll be wrong when his patience finally runs out!

There is a logical solution that guarantees they won't get executed (besides simply agreeing between them never to make the fateful assertion), and it doesn't involve waiting a long time until probability is in their favor.

hahaha that works. warden would probably be dead or promoted by then anyway

Sadistic Warden.

The 4 prisoners agree that the first time any of them go into the room, the prisoner is to turned on the switch connected to the electric chair in Ward X. If it is already on, they are to leave it alone. On any of their second visit, they are to switch it off and it is already off, they are to leave it off. Only one prisoner is to make the assertion - after something ridiculous like 30 years or 29 years and 364 days, the prisoner notices that the bloody switch has not been on for a bloody good time..he can reasonably & safely conclude that everyone's been in the room and can make the assertion that everyone has been in the room - and would be set free by the sadistic warden - and pass GO and collect $200 !!

Light bulb question. I tell my friend to go into the room which I can go in only once ( you didn't say I can't have that arrangement )...and flick the switches on one after another and ask my friend to yell out when the light is on - and therefore I find the switch that controls the light !!! Hurray !!!

wouldve been alot easier with 4 positions

Only two. Up and down, left and right, whatever you want. The switch may or may not control anything; the prisoners are so heavily guarded while outside of their cells that they wouldn't be able to tell either way, so it doesn't matter.

Oh, and the warden might be sadistic, but not so sadistic that he changes the position of the switch without the prisoners' knowledge, and he has ordered his guards that nobody may flip the switch except for the prisoners.