standard_description: Explain each step in solving a simple equation as following from the equality of numbers asserted at the previous step, starting from the assumption that the original equation has a solution. Construct a viable argument to justify a solution method.
problem_activity: Stage 3: 20 Cubes
Required Preparation
Materials to Gather
Connecting cubes
Materials to Copy
Blackline Masters
What's Behind My Back Stage 3 Recording Sheet

Narrative
Students work with 20 cubes, organized into two towers of 10 cubes. One partner snaps the towers and puts one part behind their back and shows the other part to their partner. Their partner figures out how many cubes are behind their back. Students record an addition equation with a blank to represent the missing cubes.
Additional Information
Each group of 2 needs 20 connecting cubes.


aligns: no