The methods that can aid us in estimating activity durations include: 1. Non-computational techniques, such as examining past records for similar tasks that were performed at other times in the organization 2. Non-computational techniques, such as obtaining expert opinion 3. Deriving duration estimates through computational, or mathematical, analysis; 4. Using the Program Evaluation and Review Technique (PERT), which uses probabilities to estimate a task's duration. O 2, 3, and 4 O 1, 3, and 4 O 1, 2, and 3 O 1, 2, 3, and 4