SUMIF for a range of one cell and a sum range of 242

Dear All, help greatly appreciated!

I have approx 300 sections on one worksheet. Each section has 40 individual cells, each containing a value between 1 to 12 (denoting months of the year). Alongside each of these 40 cells in each section, there are 242 columns with values in them.

What I am trying to do is SUM the values in these 242 columns in the same row opposite all the 40 cells in each section containing the value 1 to 12 (denoting months of the year).

I have entered the formula =SUMIF(C8,1,D8:IK8) and the sum returned is "0", despite there being values in the cells D8:IK8. I have also tried =SUMIF(C8,"1",D8:IK8) and =SUMIF(C8, "1", D8:IY8) I think the issue maybe that the "sum range" needs to be the same as the "range".

My question is, what formula do I need to enter if the "sum range" is much larger than the "range" (in my case 244 cells vs 1 cell).

All thoughts hugely appreciated!

Best to all.

Matt