Whole milk is 4% butterfat. How much skim milk with 0% butterfat should be added to 32 ounces of whole milk to obtain a mixture that is 2.5% butterfat?
Say you add x oz of Skim Milk. You want a mixture with 0.025 fat. You currently have 4% of 32oz of fat = 0.04(32) = 1.28
So you have,
Solve for x and you get that x = 19.2oz