I am from fourth or even fifth world country (considering the courses in my BA in Econ). I have taken only one math-related course: Linear Algebra with the mix of real analysis and one probability+math-stat course in my Econ BA. So, what can I do to cover up my gaps in terms of math? I've been admitted to Europe Econ master's but there PhD-level (mathematically rigous I think)courses starts from second year, at the time of my US PhD application I would not have taken those serious courses in MA.