I've always envied people who could do that. A friend of mine told his mathematics professor a riddle (http://en.wikipedia.org/wiki/Random_permutation_statisti

I've always envied people who could do that. A friend of mine told his mathematics professor a riddle (http://en.wikipedia.org/wiki/Random_permutation_statistics#One_hundred_prisoners http://en.wikipedia.org/wiki/Random_permutation_statistics#O...) that had taken my friend hours to logic out. The professor began talking it out and, within about 15 seconds, had produced the simple group theoretic solution that Wikipedia gives.