Reconsider Prob. 12.4-7. The management of Sunny Skies Unlimited now has decided that the decision on the locations of the fire stations should be based mainly on costs.
The cost of locating a fire station in a tract is $200,000 for tract 1, $250,000 for tract 2, $400,000 for tract 3, $300,000 for tract 4, and $500,000 for tract 5. Management’s objective now is the following:
Determine which tracts should receive a station to minimize the total cost of stations while ensuring that each tract has at least one station close enough to respond to a fire in no more than 15 minutes (on the average).
In contrast to the original problem, note that the total number of fire stations is no longer fixed. Furthermore, if a tract without a station has more than one station within 15 minutes, it is no longer necessary to assign this tract to just one of these stations.
(a) Formulate a complete pure BIP model with 5 binary variables for this problem.
(b) Is this a set covering problem? Explain, and identify the relevant sets.
(c) Use the computer to solve the model formulated in part (a).