In PERT, how is the expected duration calculated?

In PERT, how is the expected duration calculated?

• A. Most Likely is used as the sole estimate.
• B. Expected duration = (Optimistic + 4×Most Likely + Pessimistic) / 6
• C. Expected duration = (Optimistic + Pessimistic) / 2
• D. Inputs are Optimistic, Most Likely, and Pessimistic, but the formula is different.

Answer: (B)

In PERT, you combine optimistic, most likely, and pessimistic estimates using a weighted average that puts more weight on the most likely outcome. The expected duration is calculated as (Optimistic + 4 × Most Likely + Pessimistic) / 6. This mirrors the idea of a beta distribution skewed toward the most probable scenario, so the estimate tends to be closer to what you believe is most likely while still accounting for uncertainty from the best- and worst-case cases. The factor of 4 on the most likely term and dividing by 6 overall give a balanced, realistic time estimate rather than just the simple average or a single point estimate. As useful context, the same three-point inputs also define the PERT standard deviation as (Pessimistic − Optimistic) / 6, giving a measure of uncertainty around the expected duration.

In PERT, you combine optimistic, most likely, and pessimistic estimates using a weighted average that puts more weight on the most likely outcome. The expected duration is calculated as (Optimistic + 4 × Most Likely + Pessimistic) / 6. This mirrors the idea of a beta distribution skewed toward the most probable scenario, so the estimate tends to be closer to what you believe is most likely while still accounting for uncertainty from the best- and worst-case cases. The factor of 4 on the most likely term and dividing by 6 overall give a balanced, realistic time estimate rather than just the simple average or a single point estimate.

As useful context, the same three-point inputs also define the PERT standard deviation as (Pessimistic − Optimistic) / 6, giving a measure of uncertainty around the expected duration.