Go purchase a Schaum's book - they're under $15, have tons of questions, and cover the basics. You can use Wikipedia (seriously, it's very solid) to review concepts, then work through a few question in the reader.
I have a Kindle 3, and it's possible to read papers, but it's still pretty small. I'm looking at picking up something a bit bigger, probably in tablet form (or preferably with a PixelQi screen) in the next 6-8 months that would work a bit better. I haven't used the 9" DX, but I assume it would do the job better than the Kindle 3, just on basis of size.
PDFs are easy to get onto the Kindle (3, anyway): just move them onto the onboard memory, and they show up like a .azw or .mobi file would.
Example: http://www.amazon.com/Schaums-Outline-Statistics-Murray-Spie... -- $8.65