This Problem Set is a part of the Lesson 15, Unit 1, Grade 3. In this lesson, students draw arrays and pairs of tape diagrams to model the commutative property of multiplication. For example, they draw an array with 2 rows of 4 to represent 2 × 4, rotate it 90 degrees to represent 4 × 2, and then draw a tape diagram to represent each fact. This lesson focuses on multiplication involving units of 4 in order to build fluency with those facts.