Christ, Kerry, these things are getting easier and easier. [I won’t link to him (for a couple of days – see down the page), but go and check out www.riothero.com for the riddle in question] Anyway – this one took about 80 seconds. And it’s my turn to blow the answer! Read on if you dare.
Stage One: The guy at the back of the queue cannot be seeing two grey hats in front of him. If he was seeing two grey hats, then he would know that his hat had to be red. Stage Two: The guy in the middle now knows that he and the guy in front of him cannot both be wearing grey hats. Therefore, if the guy in front of him was wearing a grey hat, then he would know that he was wearing a red one. But he doesn’t know. Which means that the guy in front of him has to be wearing a red hat. The third guy having heard this exchange (and being very clever) now knows that he is wearing the red hat. If you’ll pardon my English colloquialism: Piece of Piss.