Transition from Finance to Applied mathematics
As with any application, you need to make your case. But if you have studied those three math subjects and have a good understanding of them, I think you have a basis. It might be especially possible if your future studies apply math to the financial realm, of course. 

It would be harder to get into a program with admissions systems that mostly check boxes of requirements rather than looking at individuals. If the admissions process gives you access to professors and potential advisors it would be easier, provided that you can convince someone that you can manage the early courses that might be required.