I spent an unusually long time on probability (session 2, reading 9).
Here are my thoughts:
1. the CFAI materaisl are poorly written. I've been able to easily work problems related to this same topic within other sources....but still struggle with the CFAI stuff.
2. it has a relatively low point significance on the exam, so do the best you can, then move on....don't get bogged down on it.
3. teach12.com offers a great video series on statistics.....really helpful in understanding a lot of the same concepts. I have used a lot of theri stuff and it's all good. They also offer a series on economics. Their stuff is pricey but they often run sales in which certain products are heavily discounted.
I really stressed because I finished the first 8 readings quickly but then spent about 3 weeks on reading 9. For the most part I've got it now, but I should have spent a lot less time on it than I did given its low point value on the test.