In Topic C, students develop a more robust understanding of addition word problems, moving beyond the Kindergarten problem types (K.OA.2) by reviewing put together with result unknown and add to with result unknown problems, and then moving to the more complex change unknown version of the earlier problem types. In Lesson 9, students solve both add to with result unknown and put together with result unknown problems with their classmates. The lesson begins with a cadre of students engaged in a dance party, and then a number of students join them—how fun! Students then record this action-based problem as an equation, and move on to the put together with result unknown problem type where they are faced with a set of students whose characteristics invite decomposition, much like in Topic B. Students end with a debrief where they explore the connections between these two problem types, ultimately understanding that they used the operation of addition to solve both problem types. Lesson 10 has students using 5-group cards to solve put together with result unknown problems that are represented by stories stemming from pictures. The 5-group cards again make the expectation clear that students will be practicing counting on (Level 2 strategy), but may use the strategy of counting all (Level 1 strategy) if necessary. The introduction of the add to with change unknown problem type (1.OA.6) occurs in Lesson 11. This lesson allows students explorations with problems where the action, which represents the change, is unknown. For example, “Ben has 5 pencils. He got some more from his mother. Now he has 9 pencils. How many pencils did Ben get from his mother?” Students physically add more to the starting quantity, counting on until they reach the total; for the first time in Module 1, students simply must use the valuable Level 2 strategy of counting on in order to determine the unknown part. Lesson 12 continues with solving add to with change unknown problems, as students use their 5-group cards to count on to find the unknown change in quantity. Throughout these two lessons, students explore the symbol for the unknown (1.OA.1) as both a question mark and an open box. The topic ends with students creating their own put together with result unknown, add to with result unknown, and add to with change unknown problems from equations, and having their peers solve them through drawings and discussions. These problems set the foundation early in the module for relating addition to subtraction in Topic G (1.OA.4).