I have a large amount of rows I want to sum; for which I use the SUM tool.
However, within this group of rows there are a number of rows that I don't
want to be included as part of the sum. On the contrary I want the sum of
these rows, which are the exception rows, to be added together and subtracted
from the SUM of the large group of rows.

How would I go about doing this? Any help you could give me is greatly
appreciated. Thank you.