After the students are finished, have them consider the questions in "Chew on This" as well as these other prompts:
- Did you make more mistakes in scaling the U.S. units or the metric units?
- Which set of scaled-up measurements would be easier to bake? (Is it easier to scoop out 15 cups of flour or 1.9kg?)
Aside from discussing where the two systems differ, your students may notice that the two systems are sometimes the same. For example, the number of eggs is a unit that is the same in both recipes.
You might challenge the students to think about commercial bakeries, who would not count eggs as they scale up recipes. Medium eggs differ in volume (and effects on the recipe) compared to extra-large eggs.
Students may recognize that scaling the metric system is much easier than scaling U.S. customary measurements.
Opinions will vary as to which system is better.
You would not need a scale for both recipes because the U.S. system does not require that any ingredients be weighed.