Weighted Average for Total Row

Hi guys, 

i have the following table that is not giving me the weighted average of margin as the total maring value:

The Margin (marked in red) should be a weighted value of the Margins for each articlenumber of the category CE. At the moment the Margin of 60% is just the sum of the margins underneath. Instead it should be the weighted Margin weighted with the revenue of each articlenumber:

( 100 * 0,3 + 60 * 0,2 + 50 * 0,1 ) / (100 + 60 + 50) = 0,2238 -> 22,38%

How do i maintain the table so it shows still shows the Margin for the articles as they are but for the aggregated Margin it takes the weighted Margin?

Thanks guys!