Everyday routines become easier when there is order and connection. A cake cannot be made by placing the ingredients in an oven before mixing the ingredients together. Only by following the same steps can a recipe be duplicated over and over again. The same is true when evaluating expressions.
In the activity Evaluate Algebraic Expressions, students learn that the “recipe” is to substitute a value for a variable and then use the order of operations to find the value of the expression. This includes expressions with exponents involving formulas. In the first few pages of the activity, students learn that an algebraic expression contains a variable and at least one operation, and then learn to write verbal expressions with math symbols. Since the variable in an expression can vary, students evaluate the expression using a specific value for that variable.