Why doesn't duration = work / resources

Question

I have a task that has two people working at 80% of their time on it. I have entered a task with work = 3 days. I expect the duration to be 3 / (2 x 0.8) = 1.88 days. But project insists that it is 3.05 days. I have this for a lot of other tasks in a project.

The task not effort driven and is in fixed units.

I really don't understand this. Can someone explain.

Answer 1

I assume when you say the work is 3 days - you are saying 24 hours of work. Each resource should be performing half of the work - 12 hours.

You have a couple of options to have Project calculate the correct duration:

1. In the Task Form, enter 12 hours of work for each resource. Project will correctly calculate the duration based upon Work/assignment units.
2. Remove the second resource, ensure the task is effort driven. Re-assign the second resource and Project will divide the 24 hours of work evenly - 12 hours for each resource - and re-calculate the correct duration.

If you wish Project to divide work between assigned resources, ensure your task types are effort driven and assign each resource separately.