Blanking out on tests means you're forgetting what you studied and that usually happens if you are trying to learn math by memorization. In order to stop blanking out, you must aim to understand the math rather than simply memorizing it.
The problem with memorization is that you're trying to remember how to do one form of a math question when you don't understand the fundamental math concept.
Trying to memorize something you don’t understand is 1) very difficult to do, 2) difficult to retain for any length of time, and, 3) makes it almost impossible to know how to do a question that doesn't look exactly like the one you memorized. So if you memorize without understanding, it really increases your chances of blanking out on tests or exams.
How to solve this problem? The quick answer is to start by making sure you understand the fundamentals being taught in class each day.
The first example of each math class illustrates the fundamentals of the math concept the teacher wants you to learn. Make sure you understand that first example - how it works and why.
You will know you understand the math when it starts to make sense to you, you rely less on memorization, and you blank out on tests less frequently.