This Problem Set is a part of the Lesson 8, Unit 7, Grade 4. In this lesson, students add and subtract mixed units of weight (for example, adding 4 pounds 11 ounces + 15 ounces, or subtracting 6 pounds 7 ounces - 12 ounces). They compare two strategies for composing and decomposing units in these problems, and determine which one they prefer.