This Fluency Activity is a part of the Lesson 11, Unit 4, Grade 3.<br> In this lesson, students use a given number of square units to determine all possible whole number side lengths of rectangles with that area. For example, they find by using the associative property that 4 by 12, 6 by 8, 1 by 48, and 2 by 24 arrays all have an area of 48 square units.