The divisibility rules are often “accepted without proof” by both teachers and students. The problem explored in this session involves a rich, novel way of looking at “amazing numbers,” to authentically develop notions around patterns of divisibility as a solution strategy. “This session offered opportunities for the group to use a wide range of strategies, depending on which approach a person chose in solving it. Some gravitated toward abstraction, which perhaps tilted their work toward MP7 and 8 in an algebraic sense. Others did more with modeling. All of us were involved in arguing, sense making, reasoning abstractly, and precision. All of us looked for structure and tried to apply repeated reasoning, but (as noted) some did so verbally and others with algebra. Tool-use depended on whether you used an organized list, table, visual model, or algebra.”

Algebra / Arithmetic
Number Theory

Multiple Representations
Problem Posing
Try a Smaller Problem

MP1 - Make sense of problems and persevere in solving them.
MP2 - Reason abstractly and quantitatively.
MP3 - Construct viable arguments and critique others' reasoning.
MP4 - Model with mathematics.
MP5 - Use appropriate tools strategically.
MP6 - Attend to precision.
MP7 - Look for and make use of structure.
MP8 - Look for and express regularity in repeated reasoning.