When we have variable selling overheads for marginal costing do we find the amount by applying it on units sold or on units produced and do we add it to the production cost or substract at the end like we do with absorption costing.
It is not so much that they are added to the production cost but that they are subtracted from the selling price (as are also the production costs) in arriving at the contribution.
I do illustrate this in my free lectures on marginal and absorption costing.