This Problem Set is a part of the Lesson 1, Unit 4, Grade 6. Students build and clarify the relationship of addition and subtraction by evaluating identities such as w - x + x = w and w + x - x = w. Teachers need to create square pieces of paper in order for students to build tape diagrams. If students struggled with the Opening Exercise, provide more examples before moving into the Discussion. Provide each pair of students with a collection of 10 squares, so they can use these squares to create tape diagrams throughout the lesson.