Probability theory and mathematical statistics are an applied mathematics discipline that studies a type of uncertain phenomena (random phenomena) and their regularity in the real world from a quantitative perspective. Since the century, it has been widely used in various fields such as industry, national defense, national economy and engineering technology. The random events and their probabilities introduced in this chapter are one of the most basic and important concepts in probability theory.

　　In high school, we have studied random phenomena and their statistical regularities. In college probability theory and mathematical statistics courses, we have to study such issues in depth and systematically.

　　There are two types of phenomena prevalent in nature and human social life: one type is phenomena that inevitably occur under certain conditions, which are called deterministic phenomena .

　　For example: (1) If an object falls vertically from a height of (meters), it will inevitably fall to the ground after (seconds) . When the height is constant, it can be expressed by the formula

( (m/s))

Specifically calculate the time it takes for the object to fall to the ground

 (s) .

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　　(2) Charges of opposite sexes attract each other, charges of the same sex repel each other, etc.
　　 The other type is phenomena whose results cannot be accurately predicted in advance under certain conditions, which are called random phenomena .
　　 For example: (1) Tossing the same coin under the same conditions, we cannot predict in advance whether heads or tails will appear.
　　(2) What will be the price of a certain stock on a certain day in the future? etc.
　　Philosophers have recognized the role of randomness in life since the time of Aristotle, but it was not until the early century that people realized that random phenomena could also be studied through quantitative methods. Probability theory is a mathematical discipline that uses quantitative methods to study random phenomena and their regularity.