For a telephone survey, a marketing research group needs to contact at least 150 wives, 120 husbands, 100 single adult males, and 110 single adult females. It costs $2 to make a daytime call and (because of higher labor costs) $5 to make an evening call. The file P03_30.xlsx lists the results that can be expected. For example, 30% of all daytime calls are answered by wives, and 15% of all evening calls are answered by single males. Because of a limited staff, at most half of all phone calls can be evening calls.

a. Determine how to minimize the cost of completing the survey.

b. Starting with the optimal solution, use SolverTable to investigate changes in the unit cost of either type of call. Specifically, investigate changes in the cost of a daytime call, with the cost of an evening call fixed, to see when (if ever) 50% of all calls will be evening calls. Then repeat the analysis by changing the cost of an evening call and keeping the cost of a daytime call fixed.