A system consists of two branches in parallel, each branch having two components.

The probabilities of successful operation of components A$,$ B$,$ C$,$ and D

are $0\mathrm{.}9,0\mathrm{.}8,0\mathrm{.}7,$ and $0\mathrm{.}6,$ as shown above. If a component fails, the output from

its branch is zero. If only one branch operates, the output is $50\%.$ Of course, if