The guidance system of a ship has four modules that must maintain all function properly for the system to work. Two of the modules have reliability of .85, the other two have reliability of .95 each.
a) Compute the reliability of the system.
b) A backup system with the same components will be added to the ship. The backup will be switched on automatically if the first system fails. Assuming that the switch to the backup works 95% of the time, what is the reliability of the ship's guidance system now?