Open Array Multiplication Tool. The Open Array Multiplication tool is used to demonstrate how multi-digit multiplication can be represented in various ways. Students choose from five renderings of the open array model that accommodate 2 digit x 2 digit problems and 1 digit x 1, 2, 3, or 4 digit problems. The standard algorithm is presented with a flexible ability to articulate and add partial products. Word problems can be entered to anchor each problem.