Friday, 20 May 2011
How had he worked it out?
Call the candidates X, Y and Z. X says to himself:
"Suppose my patch is white. Then Y has his hand up because he can see Z's black patch."
But also he sees Z with his hand up and, being intelligent, he asks himself: "Why is Z's hand raised? Answer: because he can also can see a black patch which must (Y will argue) be mine. IF MY PATCH WERE WHITE, the intelligent Y (and the intellgent Z) would work this out in no time. But neither has done so, since both still have their hands up. Therefore the problem is not as simple as that. Therefore my patch is black".
So X got the job.