On an island are 100 people with blue eyes, 100 people with brown eyes, and one Guru, who happens to have green eyes but that isn't relevant.
On the first day, the Guru says to everybody, "I see somebody with blue eyes." From then on, every night, anybody who knows the color of their eyes (besides the Guru, who really quite likes the island and doesn't factor into this riddle any further whatsoever) leaves.
Nobody can communicate with anybody else in any manner whatsoever. Everybody is perfectly logical. Everybody knows that everybody else is perfectly logical. Nobody initially knows exactly how many people have blue eyes or brown eyes. Nobody can directly discover the color of their own eyes (IE: by looking at some sort of reflective surface). There are, in short, no tricks. This is purely a logic problem.
How many days does it take for everybody (besides the Guru, who again quite likes the island) to leave the island?
Nov 22 2009, 8:13 pm