Summing Multiple Sums Formulas

[excel_novice01]

I have a data set that has sums for various groups within the same column, so row 1-10 will have data and row 11 will have a sum for the above numbers. Then I will have rows 12-15 with numbers and a sum formula for the data in rows 12-15, etc etc. Is there a formula that I can use to only sum the cells that have the sum formulas?

Also, the sum formulas are 'subtotal' formulas, I don't know if this will make a difference instead of using the 'sum' formula.

 

[oldbrewer]

sum the entire column and halve the result

 

[excel_novice01]

That would be double counting the numbers, since I have sum formulas midway through the data set. So since I have lines 1-10 with hard coded numbers and row 11 has a subtotal for the above lines if I up a 'sum' formula in I would be counting the numbers twice. I have like 12,000 rows of numbers so going 1 by 1 to sum each subtotal would not be economical.

 

[oldbrewer]

3
4
5
12 (sum)
6
7
8
21 (sum)
66 (sum of entire column)
33 (sum of entire column halved)
33 (sum of 3 4 5 6 7 8)