1) 1 light-bulb and 100 prisoners***
Once upon a time there were 100 prisoners, all confined in solitary cells. At the center of the prison is a strip of grass with a small cottage with a light-bulb.
One day the evil Nazi commander of the prison camp calls the prisoners together. He tells them:
“Once a day a random prisoner will be allowed to breath fresh air on this strip of grass in the center of our beloved prison. From this the lucky prisoner of the day has access to a small cottage with a light-bulb, which he can switch on or off.
When one of you thinks you have all been here at least once, and states so correctly, you will all receive free library access. If the prisoner is incorrect, you will all end up before the fire squadron.
You now have 1 evening to discuss a strategy, and then its: back to your solitary cells, and no longer any contact.”
What is a good strategy for the prisoners to decide upon?
This puzzle was first presented to me by Jon Koeter, whom I mentioned before. My fellow consultant Harrie Jans surprised me this week by solving it in 1 minute.
You can check your solution at no 210
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