How well should I know the stuff in GMAT Club mathbook?

Hi,

I am going through the mathbook composed by GMAT Club. I find the content somewhat different than what I learn from M GMAT. I haven't done any mocks yet but I don't have much time to go through 126 pages. So how well am I supposed to understand the content in the mathbook? Be able to interpret every rule/concept during the exam?

Thanks in advance.