PERT analysis is a simple form of quantitative risk analysis and can be applied to a schedule to help estimate the duration of a task. After the entry of optimistic, pessimistic, and expected durations for each of the tasks, Microsoft Project will calculate a weighted average of the three durations and determine a single duration estimate for each task. Gantt charts can display the results of critical path analysis taking all tasks at their optimistic, pessimistic and expected values. A button on the analysis toolbar provides access to PERT commands.
SOURCE; microsoft project glossary-projectlearning.net
In using the PERT method, a process by which you evaluate a probable outcome based in three ways and average the three (generally using Simpson's Rule):1. Best-case2. Expected-case, and3. Worst-case.The outcome in question may be a duration of a task,