Students will learn that variables are unknown numbers. Students have seen many missing number problems, where a blank space, or a shape was used to stand for a variable. Now we're transitioning to using letters instead, as they're much faster to write, and easier to tell apart. Next, students will learn that variables can be used to describe patterns. For example, \(a \cdot 0 = 0,\) for any number \(a.\) Then students will learn how to substitute values into algebraic expressions. For example, what is the value of \(x + 7\) if \(x = 3?\) if \(x = 11?\) For a complete lesson, watch this, this, and this. Conclude by giving your students both parts of this challenge.