Consider a small project given by the following precedence diagram and the table of times that follows the graph.
The project completion time is estimated to be 41 days with a standard deviation of 4.9 days. The estimated activity time and its respective standard deviation are shown in the table above. Task B and D has activity slack of 18.5 days without interfering the overall project completion time. Slack is basically the additional available time to complete an activity. For instance, the manager may decide to delay those activities with slack and shift resources to those critical activities to ensure overall project stability. Slack is important for resource planning purposes especially when project managers often faced with resource constraint in managing projects.