Not Able To Get Hold Of Quantitative Section

For your second issue, you might get some value out of Spaced Retrieval / Spaced Repetition as a learning method. In short, you don't just study one topic, then the next topic, then the next. Instead, you study each topic at increasingly longer intervals, to train yourself to remember it after longer and longer periods of 'down time'. For instance, when you first make a flashcard, you might study it multiple times during the first day. Then, you look at it once or twice the next day. Then, you wait two days and look at it again. If you still remember it, wait a week, etc.

Think short, varied study sessions, rather than one-topic marathons. Remembering is a skill, and if you force yourself to work hard to remember old topics, you'll get better at it.