An auditorium stage has two microphones. When turned on one has a probability of working of .90 and the other has a probability of working of .80 only a single microphone is needed to work for success if one fails when turned on the other microphone is turned on hints one of their microphones is a back up in case of the other one fails it either microphone can be treated as a back up the probability of success will be the same the probability of success is