Mathematical Thinking can be seen as a task, enrichment, or a starter in the classroom. Regardless, it is a problem that makes students think while supporting the CCSS standard listed utilizing the Mathematical Practices.
This Mathematical Thinker poses the situation of adding decimals. However, it then quickly moves into the student describing, using specific language" why certain values are incorrect.
This is designed to be used with EnVision Topic 3 Lesson 2 but will just as easily work with any lesson teaching 5.NBT.2.