Free PMI Project Management Professional Practice Question

Standard deviation (σ) measures the amount of variation or dispersion of a set of values. In PERT, it is calculated with the formula σ = (Pessimistic - Optimistic) / 6. For this task, the pessimistic estimate is 20 days and the optimistic estimate is 8 days. Thus, the calculation is (20 - 8) / 6 = 2. Since other answers may be derived from different interpretations or calculations, it is important to apply the correct formula.