Next, erase the box and write an x in its place. It stands for an unknown number. It works just like the box. We don t have to use an x. We could use any other letter we want.
Many people use x and y for variables.
Be sure to provide ample examples and exercises for students with the variable or box on the right side of the equation as well as the left. You do not want the students to always think the box will appear on one specific side. Continue with additional examples similar to the previous two. Continue with additional examples with two addends on each side of the equation. Be sure to place the variable in different positions in the equations.