First, you are a math major. If your major is ok, I suggest you take the financial engineering exam, which requires advanced mathematics and C language programming. If you can enter an investment bank after graduation, you will earn a lot. This direction is enough to learn the primary textbook of economics. Domestic postgraduate courses are generally financial integration, and foreign countries do not require economic skills;

Second, the landlord wants to take an examination of economics, but he still has no foundation at all. I suggest reading elementary books first, such as Man Kun's Principles of Economics and Gao Hongye's Western Economics. Some schools will use intermediate textbooks, such as Man Kun and Barrow, and Pindick in Xiamen University, but there is no advanced textbook for undergraduate or postgraduate entrance examination, so you should review according to the textbook specified by the school you want to apply for, but if you have enough time, I suggest reading Man Kun's Principles of Economics first, which is elementary, and then reading Man Kun or other foreign intermediate textbooks. Other subjects don't need to be studied. Specialized courses are the most important, and exams are also specialized courses. If you want to apply for other branches of economics, you should also study economics, hehe, good luck.

PS: As for the prospect, it depends on whether your postgraduate direction is academic research or business. Good prospects. Investment banks, funds and brokers are the best choices, and it is also good to enter big enterprises in the future ~