You are deciding how many independent servers to buy and which servers to buy so that a system has highest reliability. The system will be up as long as at least one of the servers is working. You have narrowed the choices to these:
A- buy one server that has reliability .9
B- buy two independent servers, each with reliability .8
C- buy three independent servers, each with reliability .7
Calculate the reliability (probability the system is up) for each of these three options.