Probability is a mathematical tool to describe the possibility of random events. In statistics and probability theory, probability is often used to describe the probability of an event. The range of probability is generally between 0 and 1, where 0 means that the event cannot happen and 1 means that the event will happen. In practical application, probability can be expressed as percentage, decimal or fraction.

For example, the result of coin toss may be heads up or tails up, so the probability of both sides appearing is 0.5, which is 50%. For another example, once you roll the dice, the probability that the six numbers 1, 2, 3, 4, 5 and 6 appear is 1/6, that is, the probability that each number appears is 16.67%.

There are many methods to calculate probability, including classical probability, frequency probability and subjective probability. Among them, the classical probability means that the probability of an event is equal to the number of times the event occurs divided by the total number of times; Frequency probability means that in a large number of experiments, the frequency of events is close to the probability of events.