I have three products that sum to a total (for this example types of milk and total milk). I am looking at units, dollars and price over two fixed time periods. I am trying to develop formulas that will determine the contibution of each item to the the total change in price. If the price for the total increased 10%, and each of the three items prices grew 5%, 15% and 20% relatively, what contribution did each make to the 10% total. Each one contributes a point change that sums to 10%, separate from their own % increases. The contribution figure I am looking for depends up the % chg for each item as well as the absolute dollar and unit sales for each item.

If anyone can create formulas for me that allow for this calculation, I will be unbelieavably grateful. And impressed.

see attached.