In many real world projects, the duration of activities is stochastic. This is why these projects are formulated as a PERT Type Network (PTN). On the other hand, completion of a project on time has a significant effect on its cost, revenue and usefulness.
Therefore, the main objective of project managers is to avoid any delay. To achieve this goal, consuming extra resources can shorten the duration of each individual activity. However, due to limitations, optimal allocation of resources among activities is vital.