Consider the system of 4 components. Componenets 1 and 2 are connected in parallel 3 and 4 are connected in series if a subsystem consists of components connected in a series then all must work correctly for sub system to work correctly. If a subsystem consists of parallel atlesst one must work correctly for the subsystem to work correctly . If components work independently of one another and p(component works ) =0.9 calculate p(system works).