Each student solved this problem using the strategy...

 that made the most sense to them. In the whole class discussion students are given the opportunity to articulate their thinking, which is valuable in its own right. More importantly, they are coming to understand the strategies of their classmates. When students begin to offer similarities and differences across methods, we see them going beyond what was asked of them—actually driving their own engagement with mathematical thinking. Even though this problem has a single right answer, we can observe students becoming more flexible thinkers as they compare and contrast strategies.