The focus of this math unit is the development of the open array as a model for multiplication and division. This unit uses a series of investigations based on the context of Muffle’s Truffles shop. The questions posed in the first investigation give students an opportunity to explore place value-the multiplicative structure of our base-ten system and quotative division. In the second and third investigations, students build two-dimensional blue prints and use these arrays to explore some big ideas in multiplication, including the distributive, associated and communicative properties. In the fourth and final investigation, students word with open arrays in the context of labeling and pricing wrapped boxes of truffles. To figure out the dimensions of the wrapped boxes (open arrays) and the cost students need to apply a number of big ideas previously developed in this unit.