How do I remove a negative sign in numbers

Do you mean you want the absolute value, something like this?

SG

You can certainly add up numbers that have a negative sign.

Are you wanting to add the positive versions (the absolute values) of the numbers instead of the actual negative numbers? If so, you can use SUMIF. The answer will be SUMIF(positive numbers) - SUMIF(negative numbers) . That's not the actual formula of course, just showing how to use it for your purpose.

Or is SUM skipping over the numbers that have the negative sign in front of them, treating them like they were zero? If this is happening it is most likely because those "numbers" are not actually numbers, they are text (strings) made up of numeric characters. The easy test for text vs numbers is that text aligns to the left side of a cell (unless you change it yourself) while numbers line up on the right side. Usually the first thing to try is to format the cells as numbers. But, given that your problem is with negative numbers, it could be the negative sign is not the correct negative sign character.

I'll stop there and wait for you to say a little more about what the problem is.