Which is the correct formula to add the values in cells A1 and B1?

I'm assuming you are referring to Excel. There are a few ways to add A1 and B1.

First you could use '=SUM (A1+B1) '

You could also use '=SUM (A1:B1) ' which adds the values of all the cells between A1 and B1, but since they are next to each other, this would work.

You could also use '=SUM (A1, B1) ' where you list all the cells you want to add with commas in between.