How do you find how many quarts of 5% butterfat milk and 2% butterfat milk should be mixed to yield 45 quarts of 4% butterfat milk?
The final solution is the addition of the fractional parts of the whole that each component contributes.
We will mix X quarts of 5% with Y quarts of 2% to obtain 45 quarts of 4%. Thus,
To calculate the ratio we use the concentrations.
Substitute our Y expression in X: