Answer:
This is a PERT (Program Evaluation and Review Technique) question and the expected duration of completing this activity can be solved using the formula below.
Pert Expected Duration Estimate = ║Optimistic Duration + (4 x Most Likely Duration) + Pessimistic Duration║/6.
15 days = Most likely Activity Duration.
10 days = Optimistic Activity Duration
20 days = Pessimistic Activity Duration
Substituting these values, we will have
(10 +(4 X 15) +20)/6. The pert estimate is therefore calculated as 15 days
The expected duration of completing this activity = 15 days.