This puzzle was posed to me by a colleague a few days ago (Thanks Christopher Geisel) and I liked it so much that I thought I would share (It’s a variant of the blue eyes problem, so many of you might already know it).
Good luck and enjoy.
There are an unknown number of monks in a chapel. They have taken a vow of silence. They take this very seriously and have extended this from not speaking to not communicating with each other in any way.
The only time the monks ever meet is for the morning prayer. All of the monks attend the morning prayer. On day 1 the chapel receives a letter from the bishop saying:
“There is a disease that has manifested itself in many of the churches. At least one of you has this disease. The disease is non-transmittable, and you will only know you have it, if you have a green face. But if you know that you do have it, you should stay in your bed to rest and not attend the morning prayer anymore”
In a normal church the monks might just look in a mirror, but this is in fact the Church of Self-Reflection! And because the monks are supposed to be self-reflective, they have of course removed all physically reflective surfaces of any kind. No mirrors, puddles or glass is to be found.
Anyways, 5 days pass and all of the monks still attend morning prayer. After the morning prayer on the 5th day, all of the monks that are sick, know they are sick and stay home. How many monks are missing from the morning prayer on day six?
What would you do?
Feel free to post your proposed solution in the comments or e-mail me (firstname.lastname@example.org).