Vincent uses 2 cups of flour for every 12 muffins that he makes. What is the total number of cups of flour Vincent will use to make 4 muffins?

If it takes 2 cups to make 12 muffins, then one cup will make six, half a cup will make 3, 1/4 will make 1 1/2 muffins, and 1/6 cup will make 1 muffin.

If you want 4 muffins, simply multiply 1/6 * 4 to get 2/3 cup.