No, there are 27 combinations(when you still account for the fact that you can have three windows machines). You can see it in that way: machine1: L, machine2

No, there are 27 combinations(when you still account for the fact that you can have three windows machines). You can see it in that way: machine1: L, machine2: W, machine3: O machine1: L, machine2: W, machine3: W The reason why it matters is that you have more ways to have exactly two linux machines: m1: L, m2: L, m3: O m1: L, m2: O, m2: L, etc. That gives you 2*3 ways of having exactly two linux machines (you have 3 ways of having exactly one non linux machine, and then this machine can be two different things). If you say that LLO is OLL, you would have only 2 ways of having exactly two linux machines. Hope this makes sense.