If you have access to the worked answers, how is it you are not able to compare the workings to yours and find out exactly where you are making the error?
If I recall the dividing of segments is directly related to what exactly it is you are trying to work out. Its been too long since I did it to offer any practical advice, but I did ring the help line and recall asking heaps of questions along the lines you are asking. That's the advantage of buying the course notes, you pay for the support.
I self studied too.....its difficult, but not impossible.
Ring the school you are studying through, they will help
Alpha