The Tale of the Green-Eyed Dragons
Here's a mind-blowing logic puzzle that my math professor shared last week. Problem A long time ago, there lived a tribe of 100 green-eyed dragons. These dragons had a rule: if any dragon in the tribe deduces what the color of his eyes was, then that dragon must commit ritual suicide by the end of that day. Aside from this, the dragons lived peacefully. Although each dragon could see the eye color of every other dragon, no dragon was cruel enough to discuss eye colors with other dragons. For all each dragon knew, he or she could be the one dragon that had blue eyes among 99 green-eyed dragons. One day, however, a visitor arrives to the tribe. On the day she arrives – we will call this day 1 – she remarks, "I see a dragon with green eyes." The visitor leaves later that day. At the end of day 1, no dragon in the tribe performs the ritual. At the end of the next day (day 2), no one performs the ritual. In fact, after the visitor leaves, the dragons continue to live in p...