Post it note substitution

Today in my math 11 class we solved systems of linear equations using post it notes. We started class by reviewing how to evaluate a variable expression. Then, I gave them two equations, y = 2x and y = 7x + 15. I had them write "Y" on two of the post it notes, 2x on one and 7x + 15 on another one. We then discussed how they both were equal to "Y" so could we move one post it note and put it over the "Y"? Yep. Now we have an equation with variables on both sides and we know how to solve that. When we got a value for "X" we wrote that on another post it and I asked them what we should do. They decided we should put it into both equations and solve for "X". That's what I did. They were amazed that it came out to the same answer in both of them. This led to a discussion on what the answer really meant (the point of intersection).
We then did a couple more examples. I allowed them to use the post it notes if they wanted to. Some used them and some caught on quickly and didn't need them. Next time I do this activity, I will give them another post it note for their "Y" value and then show them how to check their answers.