Following rules to solve the "in/out" boxes. I made the copies on card stock and laminated each one to make them sturdier for little hands to use. I used by Exacto knife to cut my slits for strips to slide through. My students enjoyed using this at our Math center, and I enjoyed the ease of checking for understanding.

The rules used addition, double, subtract, divide and multiply - I felt this would be sufficient use of operations to check for understanding.