content: The idea behind this book is great but the book itself is frustrating with how many typos and errors are in the book. By unit 12 I had given up in frustration. One of the solutions midway into the problem they forgot the superscript on one of the powers, another they changed the problem from the one written in the back to a completely different power. One of the lessons had 15 written problems to do and 16 answers in the back of the book. And yet another, and my favorite, "Do these 16 problems by yourself" Just to have them skip flat out making a problem 7!