Unless there is some common factor between the cells excel canno
operate using a sumproduct or sumif formula.
One solution would be to use a helper column to mark the ones you wan
summed.
e.g. if you added a new column A and put a Y next to all the rows yo
want summed you could then use the formula
=sumproduct((a1:a5="Y")*(d1:d5))
(remembering that column c is now column D because of addig the helpe
column
