@chinobonito Which browser are you using? You could try the free Chrome extension "Download Master" which allows you to download multiple links on a page. This worked for me and others (Mac and PC).
I'm having the same problem. I'm aware that the PDF's are gone, but the page the follows each problem set, where the answers and the video links are to be found, seems to have disappeared.
Hey everyone, sorry for the confusion. The new problem sets are from 17-35, and the video explanation links are all back now. More information in this thread: