In this lesson, students partition segments in given ratios. They begin by connecting prior work with midpoints to partitioning in a ratio and are introduced to a new notation for finding an average between two endpoints. Next, students are introduced to a weighted average and partition segments into other ratios. As students attempt to partition segments using multiple methods, they are making sense of problems involving weighted averages in the coordinate plane (MP1). Finally, students link segment partitioning and weighted averages to concepts of similarity transformations from earlier units.