a computer system is designed so that if component c1 fails, it is bypassed and c2 is used. if c2 fails, then it is bypassed and component c3 is used. if c3 fails, then it is bypassed and component c4 is used. the system fails only if all 4 components fail. the failure of any of the four components is independent of the failure of any of the other components. there is a .4 probability that c1 fails, a .4 probability that c2 fails, a .3 probability that c3 fails and a .2 probability that c4 fails