Estimate Durations

Give an example of an activity where duration cannot be determined with absolute certainty.  For that example, provide an optimistic, pessimistic and most likely duration.  How might you estimate these durations? How do you determine the Early Start for an activity with two predecessors?  How do you determine the Late Finish for an activity with two successors?As a project manager, would you manage the critical path tasks differently than non-critical tasks? Why, or why not? If yes, what would you do differently?Beyond the apparent simplicity, briefly explain why do most PMs use MSP’s Gantt chart format more often than the network format?