Peace, googling for it, it seems like it is a .Net library that protects against division by zero: http://msdn.microsoft.com/en-us/library/dd578496.aspx Assuming it is the same library that you are using, if division by zero is not a consideration, you can use=Sum(Fields!A.Value)/ Sum(Fields!B.Value)
If the denominator happens to be zero, I think the report will show Infinity. If you want to avoid that, you can use an expression depending on what you want to display in that case.