How to average a list of cells to include blanks, but also allow me to insert new rows and keep formula

[Robjwalters]

I have a project plan. I want to track the progress of the subtasks. I thought just averaging them would work, but it does not. If I have 6 subtask, and any of those are 100%, then my progress tracker shows 100%. It shouldn't show that unless all tasks are done.
I have it formatted as a table, which I was hoping would allow my formula to update as I insert rows.
In my example file:
In Cell C2, I want the average of C3-C8.
IF I insert a row above row 9, the formula needs to update to include that cell.
(I understand that if I add a row in between row 3-8 that the formula will update)

Just not sure how to get it to update if I add in another row.

 

[vletm]

Could You add/use Total Row to Your table?
... and select to show average.
... after that You can delete that C2-cell formula.
Or
Do You have an idea to have there many ... Sections?
Or
Should those precent complete need to be in same table?
... You could get those from Pivot-table (need to modify Your current table)
>> Show what do really You should have there?