I have 3 columns, I want column A's rows to be summed and then the result to be subtracted from the sum of column B and then the result to be shown in column C.

Whatever formulae I write keeps giving errors and nothing works!

Switch columns: move column A data into column B and column B data into column A?

sorry, I don't understand how that's going to work!

right now I wrote this but it doesn't work
=SUM(A3:B999)-(B3:B999)

I Googled and found this:

The Joel on Software Discussion Group (CLOSED) - How to subtract two columns in Excel? (http://discuss.joelonsoftware.com/default.asp?joel.3.367037.13)