There are 362880 ways for rabbits to eat radishes according to 1 to 9. A ***9 radishes, according to the arrangement and combination, there are 9 choices for the first time, and there are 8 left after eating the first one, so there are 8 choices, 7 for the third time, 6 for the fourth time, and so on. The walking method is 9 times 8 times 7 times 6 until it is multiplied by 1, and the calculated sum is the total walking method, which can calculate 362838.

Permutation and combination is the most basic concept of combinatorics. The so-called arrangement refers to taking out a specified number of elements from a given number of elements for sorting. Combination refers to taking out only a specified number of elements from a given number of elements, regardless of sorting. The central problem of permutation and combination is to study the total number of possible situations in a given permutation and combination. Permutation and combination are closely related to classical probability theory.

Although mathematics began in ancient times, there was no skill because the development of social production level was still in the low stage. With people's understanding and research on numbers, in the process of forming mathematical branches closely related to numbers, such as the formation and development of number theory, algebra, function theory and even functional, the diversity of numbers is gradually discovered from the diversity of numbers.

Typical example

Grandpa's family has 12 radishes. Grandpa will feed a radish to every small one in the family. Finally, there are three radishes left. Q: How many rabbits does Grandpa have at home?

Answer: 12-3=9 (only)

The teacher brought 20 books and gave them to every child in the classroom. There are still four books left. How many children are there in the classroom? Answer: 20-4 equals 16 (Ben)

The school bought 20 skipping ropes and gave one to each student who participated in the skipping competition, but the result was still 4. Q: How many children took part in the skipping competition? Answer: 20+4=24 (person)

The teacher brought 20 books and distributed them to all the children in the classroom. There are still six books missing. How many children are there in the classroom? Answer: 20+6 equals 26 (pieces)