The question at
asked for the average, i.e. the mean, number of letters that would be left unchanged in position if the letters of 'Dermatoglyphics' are scrambled at random. The answer is 1 and surprisingly, to me anyway, the answer would be exactly the same for any other word with no repeated letters, whatever its length. Even though I know why this is it still amazes me, it seems to go against intution.