marking formula

Hi. I need some help coming up with a formula. I had a working version a few years ago but somehow I seem to have lost it. I have a spreadsheet with student marks. What I am having trouble with is if a student is away I need to deduct that quiz from the total (the total shows up in several other locations). I usually record a "sick" in the cell rather than a number so I need a program which looks for "sick" or any other characters rather than numbers and then finds the appropriate quiz total and deducts that from the cumulative total. I also need to deduct the new totals from any other total which refers to it. I hope this explanation is clear. Please help since doing this manually is a real pain. Tom

Thanks for your quick response. I hope the following spreadsheet makes sense. Please delete this when you are finished. Tom

Hi,
I have attached a simplified version of my marks spreadsheet. Columns C to N are the marks for one set of quizzes. Columns O through Z for another set. The first set are all out of 10 while the second set has a variety of totals. Columns M and Y reflect the totals for each student on those sets of quizzes. m$2 and z$2 are the total possible marks for each set of quizzes respectively. What I need is when someone is sick, the totals m$2 and z$2 should not include the quizzes that that student missed due to being sick. The totals should remain the same for those who were not sick. I hope this is clear. Thanks again. Tom

I am not sure the attachment was included with the previous post. Here it is.

Thank you for your help. Your formula works great if the quiz total is always the same. What about if the totals are constantly changing as in the case of the second set of quizzes in columns O - W. I really do appreciate your help. Tom