What is the the average percentage of profit for the all the product?
average profit percentage = DIVIDE(SUBTRACT(ListPrice, StandardCost)), (StandardCost)));
SELECT AVG((T1.ListPrice - T2.StandardCost) * 100 / T2.StandardCost) FROM ProductListPriceHistory AS T1 INNER JOIN ProductCostHistory AS T2 ON T1.ProductID = T2.ProductID