In a previous unit, students solved Add To, Result Unknown and Take From, Result Unknown story problems. In Put Together, Total Unknown story problems, there are 2 groups of objects, rather than 1 group of objects with more added or taken away. Because there are 2 groups of objects (such as red apples and green apples), students may distinguish between the 2 groups in a variety of ways, such as:

• drawing pictures of the different groups
• separating the groups
• using 2 different colors
• using letters, words, or numbers as labels

Students may have used some of these representations in the previous unit. While it is not important for students to use any particular method, they should be able to communicate how their representation shows the story (MP6). The purpose of the lesson synthesis is for students to think about how to improve their representation.

In Unit 4, students solved Add To, Result Unknown and Take From, Result Unknown story problems. How did that work prepare students for the work in this lesson? How are Put Together, Total Unknown problems different from the story problems students have worked with?