The recipe calls for 1/2 cup of flour to make 8 servings. How many cups of flour are needed to make 20 servings. Explain.

1 and 1/4 cups, because for every 8 servings, you have 1/2 cup of flour, so if you make 16 servings, you have one cup. Since 16 plus 4 is 20, and half of 8 is 4, you would need to have 1/4 cup more to half the number of servings.