This lesson is optional because it does not address any new mathematical content standards. This lesson does provide students with an opportunity to apply precursor skills of mathematical modeling (MP4).

In previous lessons, students learned that an array is an arrangement of objects into rows with an equal number of objects in each row. They determined how many objects were in an array and represented the number as a sum of equal addends. In this lesson, students use what they know about arrays to show different ways chairs could be arranged for a school band concert. Students may represent the arrays and the total number of chairs in any way that makes sense to them. They then think about which array would be the best for this situation and make a recommendation for how the seats should be arranged.