Final answer:
In the context of an elementary school with 680 students, the most logical assumption is that there are 20 classrooms. This figure makes sense given typical school sizes and class sizes.
Step-by-step explanation:
The question seeks to find what there are 20 of in the context of an elementary school with 680 students. Based on the information provided, the most logical conclusion is that there are 20 classrooms. This is because the number of teachers, grades, or subjects typically would not be a fixed number like 20 in relation to the total number of students. In a typical elementary school setting, there could indeed be around 20 classrooms to accommodate 680 students, depending on class size. Without more context, this is a best guess rather than a definitive answer.