I have to add my students marks in say cells C5, C9, C15 and C 36 in
C50 (formula used =Sum(C5, C9, C15, C36)

Since the student was absent for one assessment his marks are 40, 55,
Ab and 30. I wish to add these four cells and get the valid total but
the prsence of Ab in one of the cells of the formula gives me an
invalid answer in the total cell.

I know that I can mark a zro instead of the absent but I use a zero
when a student is present and has actually got ')' marks in an
assessment while Ab is meant to remind me of his non-arrival!

Anyway i can work this my way??

Thanks