This product was designed for a unit on addition and subtraction with regrouping. I used this to introduce to the students HOW to identify a problem that regroups and a problem that does not.
We first talked about why an addition problem (or subtraction problem) would need to be regrouped. Then, I had the students look at each problem and either write "D" for "Don't Regroup" or "R" for "Regroup" in the gray boxes on the worksheet.
A few weeks later, once the students had more practice with addition (or subtraction) with regrouping, we revisited this activity. I had the students take their squares out of each bag, solve the problem, and determine if they had sorted it correctly or not.