excel – SumProduct with division?

I have 2 columns that span across many rows. What I need to do is calculate the percentage of each row and then add them. Setup is something like:

ColA      ColB
5         5
10        
          10
3         7

The total for ColA, should be calculated like (5/(5+5))+(10/(5+5))+(0/(0+10))+(3/(3+7)). I have a formula which works in:

=SUMPRODUCT((A2:A1000)/(A2:A1000+B2:B1000))

The problem is that if there are blank values in both rows, then it gives the #DIV/0 error because you can’t divide by 0. How would I write the formula to exclude rows where both are blank?

EDIT:
Some actual data and expected values are:

ColA      ColB
40      
          40
35      
          35
35      
          35
          35
35      
17.5      17.5
          40
40      
          40
40      
7.5       28.5
36      
          36
36      
36  

When totaling ColA, should be 9.7
When totaling ColB, should be 8.3

Tags: excelexcel