An online video game has five servers. For each server, the probability of it working on a given day is 0.9. The game developers decided that if two or fewer servers are working, the game will shut down, otherwise, it will continue. It is reasonable to assume that the servers are independent of each other. Given that the game is not shut down, what is the probability that all 5 servers are working? In the answer sheet it says the probability is 1/(n-1) * ∑(x(i)-x(bar)), but I don't understand that and it doesn't actually give the answer, just this formula. So what is the answer and how do I come up with it?