A reader at the Math 1 level has enough mathematical ability to encompass “good at math” in a colloquial sense. They know at least some basic algebra, and how to apply algebraic thinking to problems in some contexts. If you threw a simple to moderate math puzzle at them, they could probably figure out what they were supposed to do without balking and saying “nope, I don’t know how to do this”.
Writing for a Math 1 audience
At this level, you can start to use letters to represent numbers as variables and manipulate them directly.
Mathematics is the study of numbers and other ideal objects that can be described by axioms.