ad 11.
I think that all the possible "combinations" are not 27 but 10, because e.g. tuples (Linux, Windows, Linux) and (Linux, Linux, Windows) are identical. I.e you should count combinations not variations.
All the poss combinations:
LLL, LLW, LLO, LWW, LWO, LOO, WWW, WWO, OWO, OOO
Then you cross out WWW (xterm constraint), and you have 9 combinations, of which 3 are valid for the condition (at least two "Ls"). So 1/3.
Let me know if I got sth wrong :).