fullchandra,
As far as I am aware, there isn't such a compilation of gmatprep explanations floating around.
However, I believe most of the gmatprep questions have already been answered (at least once) in this forum. So, if you'd like to see explanations to these problems, you could run a keyword search using the search bar at the top.
If you still can't find anything, then post the problem. I'm sure it will be answered within a couple of hours (if not minutes!).
Welcome to BTG!
-BM-