HAL Corporation manufactures large computer systems and has always prided itself on the reliability of its System 666 central processing units . In fact , past experience has shown that the monthly downtime of System 666 CPUs averages 41 minutes , and has a standard deviation of 8 minutes . The computer center at a large state university maintains an installation built around six System 666 CPUs . Mr. Joe , the director of the computer center , feels that a satisfactory level of service is provided to the university community if the average downtime of the six CPUs is less than 50 minutes per month . In any given month , what is the probability that Mr. Joe will be satisfied with the level of service ?