How can i get a better grasp of the math fundamentals?

To get a better grasp of math fundamentals, you could go back and review your course materials. You can also look at additional resources, since it can be useful to see the same concept presented in a variety of ways.

You can also use the tagging feature on the BTG forums to focus on one concept at a time. For example, here are all of the questions tagged as statistics questions: https://www.beatthegmat.com/forums/tags/ ... statistics (see the left side of that linked page for more tag options)
Focusing on one concept at a time will allow you to see core concepts in action, and it will let you see the various types of questions that can be asked about a certain concept. I also suggest that you spend a lot of time reviewing the responses from the Experts on this site. They model the steps you should be taking when tackling math problems.

Cheers,
Brent