The emergency services coordinator for Dade County, Tallys DeCampinas, is interested in locating the county's two ambulances to maximize the number of residents that can be reached within 4 minutes in emergency situations. The county is divided into six regions, and the average times required to travel from one region to the next are summarized in the following table:

The population (in 1000s) in regions 1 through 6 are estimated, respectively, as 21, 35, 15, 60, 20, and 37. In which two regions should the ambulances be placed?
a. Formulate an ILP model for this problem.
b. Implement your model in a spreadsheet and solve it.
c. What is the optimal solution?
d. How many ambulances would be required to provide coverage within 4 minutes to all residents?
e. Suppose the county wants to locate three ambulances in such a way to provide coverage to all residents within 4 minutes and maximize the redundancy in the system. (Assume redundancy means being able to provide service by one or more ambulances within 4 minutes.) Where should the ambulances be located?

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