Formula average

1 product

3 Prices for the same product (ordinary/student/member)

                    Ordinary        Student         Member

Prices              82                   54                   44

% of sale.       33%.                53%.               14%

So it's one product, but with three different prices. I want to find the average outgoing price for that product, when i sell the product for different prices... 

F.ex.:

                    Ordinary        Student

Prices                100               50

% of sale           50%             50%

This would mean that the average outgoing price for the product - depending on how much the different prices sells - is 75.