This activity introduces simplifying expressions. I have created shapes. to help students understand the meaning of a variable. The shapes are the containers and the the variable is what they contain inside. For example: If you look on the answer sheet you will see 5 different shapes. Circles have the same amount of skittles or paperclips inside. That is the variable. The unknown number of skittles or paperclip or whatever you chose to use. Triangles all have the same amount of skittles (probably different amount than the circle container unless a = b; maybe the triangle containers are jumbo skittles or paperclips).
Have fun with it!