A little puzzle

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For my last entry into this section before I hand over management of the website to John Meyer, I thought I’d share a favourite puzzle of mine with you. The below text is adapted from the blog of Terry Tao.

On a remote island in the Pacific, there is a tribe of 1000 people, 100 of whom have blue eyes and 900 of whom have brown eyes. The tribe is highly religious and one strict law of their religion is that they are forbidden from knowing their own eye colour or even discussing the topic with one another, though each tribesman can see the eyes of every other tribesman. The island is even devoid of reflective surfaces to prevent tribesmen from accidentally discovering their own eye colour, since if any member of the tribe does discover the colour of his eyes, the religion requires him to commit ritual suicide at noon the following day in the village square for all to witness. Prior to joining the tribe, all prospective members are required to undergo intense training in logic. In the village square, where daily prayers are carried out, it is inscribed on the tablet of holy laws, together with the rule about eye colour, that no person may be a member of the tribe without having first demonstrated that he is flawlessly logical and entirely committed to the laws of the religion.

One day, a blue-eyed foreigner visits the island and wins the complete trust of the tribe. That evening, he addresses the entire tribe to thank them for their hospitality. However, not knowing the local law, the foreigner mentions eye colour in his address, saying that “it’s wonderful to see another blue-eyed person like myself in this region of the world.”

What effect, if anything, does this faux pas have on the tribe?

Think about this yourself for a bit, then click here to unmask some further comment.

If you want to read any more about this problem, there’s plenty to be found using Google.

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