This Instructional Activity is a part of the Lesson 5, Unit 4, Grade 8. In this activity, students investigate a number puzzle. After the puzzle is demonstrated, students are tasked with figuring out how it works and encouraged to create an algebraic representation of the puzzle. The goal of this activity is to build student fluency working with equations with complex structure. This activity also looks ahead to the future work on functions where students will revisit some of these ideas and learn the language of inputs and outputs. More immediately, this activity points to the study of equations that do not have a single answer, which students will learn about in more depth later in this unit.