How can I sum a column based on the value of the column next to it. Let me explain:
Column A contains a number, and I want to sum column A1 to A100, but only for those cells where the corresponding B column contains an 'X'. So if B1 contains X then A1 would be part of the sum if B1 does not contain an X then A1 is skipped. And this would be so for each row.