Online versions of Art of Problem Solving Textbooks are now available http://www.artofproblemsolving.com/store/online . The online books have the content of the printed text and also videos. Looking at a sample page http://www.artofproblemsolving.com/ebooks/prealgebra-ebook/preview , I was a little surprised that there is a button to "show solution" after you have entered your answer but not to automatically check you answer, as most online math programs do.