Final answer:
The number of egg whites used is proportional to the cups of jelly used in the jelly frosting recipe because they maintain a constant ratio. By keeping the amount of egg whites in the same ratio to the amount of jelly, the recipe can be scaled successfully.
Step-by-step explanation:
Proportionality in Recipes
To determine whether the number of egg whites is proportional to the cups of jelly used in a jelly frosting recipe, you must see if there is a constant ratio between the two ingredients. The recipe calls for 1/3 cup of jelly for every egg white. If you were to scale up the recipe, for every multiple of 1/3 cup of jelly you would use, you would need the same multiple of egg whites to maintain the recipe. For example, if you use 2/3 cup of jelly, you would use 2 egg whites, maintaining the ratio of 1/3 cup of jelly per egg white. This shows a proportional relationship between the cups of jelly and egg whites.
If we consider the pancake recipe provided, where a batch calls for 2 cups of pancake mix, 1 egg, and 1/2 cup of milk, and we want to make more batches, we would keep these proportions the same. Similarly, for the pound cake recipe, if you increase one ingredient, you must increase all other ingredients in the recipe equally to maintain the proportionality, such as 4 pounds of butter requires 4 pounds of each other ingredient.
Therefore, the use of egg whites is indeed proportional to the amount of jelly. A proportional relationship in cooking ensures that the recipes are scalable, and the end product maintains its intended texture and taste.