(2) Impossible event: An event that will not happen under condition S is called an impossible event relative to condition S. ..
(3) Deterministic events: inevitable events and impossible events are collectively referred to as deterministic events relative to condition S. ..
(4) Random events: events that may or may not occur under condition S are called random events relative to condition S. ..
(5) Frequency and number of times: repeat the test for n times under the same condition S, and observe whether the event A appears, and call the number of times that the event A appears in n times of testing as nA event.
Related introduction:
In a specific random experiment, every possible result is called a basic event, and the set of all basic events is called a basic space.
Random events (events for short) are composed of some basic events. For example, in a random experiment of rolling dice twice in a row, z and y are used to represent the first and second appearance points respectively. Z and y can take the values of 1, 2, 3, 4, 5, 6, and each point (z, y) represents a basic event, so the basic space contains 36 elements.
"The sum of points is 2" is an event, which consists of a basic event (1, 1) and can be represented by the set {( 1, 1)}. "The sum of points is 4" is also an event, which consists of (1, 3.
If "the sum of points is 1" is also regarded as an event, then it is an event that does not contain any basic events and is called an impossible event. P (impossible event) =0. This event can't happen in the experiment.
If "the sum of points is less than 40" is regarded as an event, which contains all the basic events, and this event must occur in the experiment, it is called an inevitable event. P (inevitable event) = 1. In real life, it is necessary to study various events and their relationships, and subsets of various elements in the basic space and their relationships.