The probability is difficult. In advanced mathematics, function segmentation, definite integral, indefinite product order and its function property set, sum of numbers, double integral, even their differential definitions and linear algebra are used. If linear algebra is the thirteenth chapter of higher mathematics (it is said that it has been done in the textbook), then probability is the application of the previous disciplines, so it is more difficult and requires a lot of calculation ~ engineering, economics, probability theory and mathematical statistics in life. In life, there are still not many people who use high numbers directly, and high numbers are only the foundation of the foundation ~