The pH of most yogurts is somewhere between 4.0 and 5.0. Because optimal pH tends to be the pH of the solution, the optimal pH of yogurt would be between 4.0 and 5.0 as well.

It is usually the answer in linear programming. The objective of linear programming is to find the optimum solution (maximum or minimum) of an objective function under a number of linear constraints. The constraints should generate a feasible region: a region in which all the constraints are satisfied. The optimal feasible solution is a solution that lies in this region and also optimises the obective function.

It is usually the answer in linear programming. The objective of linear programming is to find the optimum solution (maximum or minimum) of an objective function under a number of linear constraints. The constraints should generate a feasible region: a region in which all the constraints are satisfied. The optimal feasible solution is a solution that lies in this region and also optimises the obective function.

In the sentence "The amount of feedback that students receive is not optimal", the word "optimal" is an adjective, more specifically a predicate adjective modifying the simple subject of the sentence, "amount". The word "optimum" does not occur in the sentence, although "optimal" could reasonably be called an adjective corresponding to the noun "optimum". In informal speech, "optimum" itself is often used as an adjective, but "optimal" is preferable for the adjective form.

The optimal solution is the best feasible solution