I'm using Excel X (on Mac) to do some survey statistics. Each row
contains a question and the following six columns contain the number of
responses for each of A, B, C, D, E and N/A. The next column contains
a formula to calculate a weighted average of the responses, where A
counts as 5 points, B as 4 points, etc. I want to leave any N/A
responses out of the calculations so my formula is:

=(C11*5+D11*4+E11*3+F11*2+G11*1)/(C11+D11+E11+F11+G11)

As I get new surveys to compile, I just clear out the old responses (in
C11:H41) and then start typing in the new counts. The really annoying
thing is, if I enter a number into the H column (to track the N/A
responses) Excel will automatically edit my formula (in column I) to:

=(C11*5+D11*4+E11*3+F11*2+G11*1)/(C11+D11+E11+F11+G11+H11)

My question: Why is it doing that?!?! And how can I get it to stop?!