The activity flexibility option is incorporated into the new model by defining two
routing alternatives, route 1 and route 2 that include only two activities. The model can
be modified to include more than two activities in one route. In addition, future research
is needed to include more than one activity flexibility option to the proposed model.
Dependencies among the different flexibility options should also be considered while
conducting this future research. Furthermore, this study demonstrates how to include an
outsourcing alternative for one activity in a product-mix decision problem. Extending the
model to include more than one outsourcing option is possible.