Do we keep ratios as measures in cubes or do we keep the pieces and then calculate the ratio in the report
so if A=b/c then do we have A in the cube or just b and c and then calculate A in the report
You can do that in the cube also but that is a generic answer. Typically, calculated mesures are created in Transformer only when you have to calculate something from different data sources. If the columns required for the calculation are present in the same data source (Query subject) it is preferable to do that in the Query itself.