As strange as this may sound, this was one of my favorite lessons. I’ve taught solving linear inequalities for years, but I never really thought of the properties of inequalities. I knew them and of course knew the rule of switching the inequality sign when multiplying both sides (or dividing) by a negative. But, I had never framed it as a property issue, which it clearly is. So, I like that more technical basis of understanding the process. I don’t know if the kids will share my enthusiasm.