A project activity involves digging a large number of post holes deep into the ground. When you ask the team that will be responsible for completing this activity to develop an effort estimate for the project schedule, they respond that the effort is driven significantly by the specific soil conditions.
From history, they tell you that about 20% of the holes will take 20 hours each, 70% of the holes 40 hours and 10% of the holes 100 hours each.
What is your effort estimate for the activity and why?