The P-center problem requires that all demands be covered within the distance determined by the model. Formulate a variant of the P-center problem in which the objective is to minimize the distance,...

The P-center problem requires that all demands be covered within the distance determined by the model. Formulate a variant of the P-center problem in which the objective is to minimize the distance, Q, such that 100a percent of the demand nodes are covered within Q distance units. Clearly define all sets, inputs, and decision variables. State both the objective function and all constraints in words as well as in notation.