It takes 3 minutes to load and 2 minutes to unload a machine. Inspection, packing, and travel between machines totals one minute. Machines run automatically for 20 minutes.

Operators cost $12 per hour; machines cost $30 per hour.

a. What is the maximum number of machines that can be assigned to an operator without creating machine idle time during a repeating cycle?

b. What assignment minimizes the cost per unit produced?

c. If four machines are assigned to an operator, what will be the cost per unit produced?

d. For what range of values for concurrent activity is the optimum assignment equal to four?

e. If 15 machines are needed to meet the production requirement, how should they be assigned to operators in order to minimize cost per unit produced?