=12.20. For the Dupit Corp. case study introduced in Section 11.4, the management science team was able to apply a variety of queueing models by making the following simplifying approximation. Except for the approach suggested by the vice president for engineering, the team assumed that the total time required to repair a machine (including travel time to the machine site) has an exponential distribution with a mean of two hours (1

⁄4 workday). However, the team was somewhat uncomfortable in making this assumption because the total repair times are never extremely short, as allowed by the exponential distribution. There always is some travel time and then some setup time to start the actual repair, so the total time generally is at least 40 minutes (1

⁄12 workday).