standard_description: Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.
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