In this lesson, students solve two types of word problems: "add to with result unknown" (for example, "There are 4 students dancing at a party. After a little while, 1 friend came along and joined the party. How many students are dancing at the party now?") and "put together with result unknown" (for example, "5 students were sitting, and 2 students were standing. How many students were there altogether?"). The lesson ends with a discussion in which students reflect on connections between these two problem types, recognizing that they use the operation of addition to solve both.