OP,
Re: “actuarial science” and “grad school”?
As I posted, I do not know. In my guess though, mostly you need to pass a series of rigorous tests, but I do not know how to prepare for such a test.
I actually heard that almost all economics courses have a high demand on student’s applied math background (definitely at the level of multivariable calculus and linear algebra.) after the student has passed the economics 101 class. So it is no harm to have a strong background in applied math if you may major in economics. (One of DS’s professors actually advised their students to take at least one math class every semester in college if a STEM-related grad school will be in their plan.)