A26=6x5

In the case of a, the upper 2 is equivalent to the number of digits, and then multiplied by the lower 5. In the case of 2, it is equivalent to multiplying by 2, that is, 5×4.

If it is C, it is divided by 2 on the basis of A! , that is, 6x5/(2x 1)

Extended data:

Probability theory is a branch of mathematics that studies the quantitative laws of random phenomena. Random phenomena are relative to decisive phenomena. The phenomenon that a certain result must occur under certain conditions is called decisive phenomenon. For example, at standard atmospheric pressure, when pure water is heated to 100℃, water will inevitably boil.

Random phenomenon means that under the same basic conditions, before each experiment or observation, it is uncertain what kind of results will appear, showing contingency. For example, when you flip a coin, there may be heads or tails. The realization and observation of random phenomena are called random experiments. Every possible result of random test is called a basic event, and a basic event or a group of basic events is collectively called a random event, or simply called an event. Typical random experiments include dice, coins, playing cards and roulette.

The probability of an event is a measure of the possibility of an event. Although the occurrence of an event in random trials is accidental, those random trials that can be repeated in large numbers under the same conditions often show obvious quantitative laws.

The following is the axiomatic definition:

Let the sample space of random experiment E be ω. If the real number P(A) is assigned to each event a of e according to some method, and the following axioms are satisfied:

(1) Nonnegativity: p (a) ≥ 0;

(2) Normality: p (ω) =1;

(3) Countable (complete) additivity: For an infinite number of countable events A 1, A2, ..., one, ..., which are mutually incompatible, there are

The real number P(A) is called the probability of event a.

It should be mentioned that the following nine theorems for calculating probability have nothing to do with the calculation of the above-mentioned events. All theorems about probability are derived from three axioms of probability, which are applicable to all probability theories including Laplace probability and statistical probability.

Theorem 1: Also known as complementary law. The probability that an event complements a is always 1-P(A).

The probability of not appearing red in the first round is 19/37. According to the law of multiplication, the probability that the second rotation does not appear red is, so the complementary probability here refers to the probability that at least one of the two consecutive rotations is red, right?

Theorem 2: The probability of an impossible event is zero.

It is proved that Q and S are complementary events. According to axiom 2, there is P(S)= 1, and then according to the above theorem 1, P(Q)=0 is obtained.

Theorem 3: If A 1 ... an event cannot occur at the same time (mutually exclusive events), but several events A 1, A2, ... a ∈S are in the relation of empty sets, then the probabilities of all these event sets are equal to the sum of the probabilities of a single event.

For example, in a roll of dice, what is the probability of getting 5 or 6 points?

Theorem 4: If events A and B are difference sets, what are they?

References:

Baidu encyclopedia-probability theory