Whoever is good at math tells me why this problem is calculated this way?

First of all, one of the five couples is randomly selected to sit down, and the others are then seated. Then a(9,9) is the total of all possible things that everyone else is sitting casually on. Numerally, there is a c(2,1), which refers to the choice of husband or wife at the beginning.

a(4,4) refers to the information of the remaining 4 pairs of people. a(2,2) refers to the fact that there are two internal orders of husband and wife.

If you don't know, you can ask.

10 people do it at will, the denominator should be a(10,10), not c(10,10) can also be understood like this:

10*c(2,1)*a(2,2)*a(2,2)*a(2,2)*a(2,2)*a(4,4)/a(10，10）

Actually, it's the same as above.

One of the randomly selected pairs sits down, and the others are seated. In this way, 10*2*c(2,1) ,2)*a(2,2)*a(2,2)*a(2,2)*a(4,4) are the remaining four pairs in order.

The denominator is a(10,10), and because it is arranged by position, it cannot be ignored as c(10,10).

The problem with this topic is too big ... First of all, will the wedding organizer assign one man and one woman to each table, or may only assign one person, or no person. Once you have figured this out, you can continue to do it.

And the a99 in this solution means that only one person can sit at a table. So...

The meaning of the question is inferred from the answer, that is, the probability that 5 men and 5 women will be in 10 adjacent positions and next to their partners. In this case, let's try this method, the first seat, sit casually, the probability is 1. The second seat, choose one of the remaining 9, so it's one in nine, the third seat is free, the fourth seat is one out of 7, one in seven, and so on, and the final answer is 3*5*7*9/1...

It's 2 times worse than your answer. I don't know what's going on.

20 small tables, 30 small stools, small tables are 8 yuan more expensive than small stools, and 2860 yuan are shared.

Solution: Because the small table is 8 yuan more expensive than the small stool, so assuming that the ** of the small stool is x yuan, then the ** of the small table is (x+8) yuan, so .

30x+(x+8)×20＝2860

30x+20x＝2860-20×8

30+20)x＝2860-20×8

x (2860-20 8) (30+20) solution: x 34

That is, the small stool ** is 34 yuan, and the small table ** is 34 + 8 42 yuan.

Solution: Each small table is 8 yuan more expensive than a small stool, and 20 small tables are 8x20 = 160 yuan, 1860-160 = 1700 yuan. This 1700 yuan is the sum of the small stool and the small table under the same ** 1700 (20 ten 30) = 34 yuan, and the small table ** two 34 ten eight two 42 yuan.

1.Choose 6 numbers from 1 10, and the sum of two of them must be 11Can you tell the truth?

Group these 10 numbers, (1,10); (2,9);(3,8);(4,7);(5,6), these 5 groups of numbers are regarded as 5 drawers, then take 6 numbers only less than one drawer in the two numbers are taken out, so from 1 10 these 10 numbers choose 6 numbers, of which there must be two numbers of the sum is 11

2.Write any number "0" or "1" in each of the following boxes, and at least how many columns of numbers are exactly the same?

You don't have a diagram, so you can't answer it.

Blind Zheng 3 + 7 + 9 + 11 + 13 +...9 is calculated, then divided by 2, and if the division is an integer, then look for the first number.

If the fruit of the rotten song is divided into a decimal number, then take the number next to that number, and the two gods can pick up the number.

i is greater than u, 9x 7i is greater than 9x-7u, so 7i is greater than 7u, i is greater than u