How many three digits can be made up of three digits? Four digits and five digits? What rules do you find? Six, seven and eight digits?

High school permutation. Is there zero 9 * 9 * 8 at the top, 9 * 9 * 8 * 7 at four, and 9 * 9 * 8 * 7 * 5 at five

What are the maximum ten digits of the multiple of 99 made up of the ten numbers 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9

0 + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45, which is a multiple of 9
Arrange the above ten numbers into a multiple of 11, and take the maximum
39 - 6 = 33, the sum of odd bits is 39, the sum of even bits is 6, so it is not the largest
28-17 = 11, the sum of odd bits is 28, and the sum of even bits is 17
nine billion eight hundred and seventy-six million five hundred and twenty-four thousand one hundred and thirty
This number should be the largest

It can be made up of ten numbers: 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9______ Three digits without repetition

9 × 9 × 8 = 648, a: it can make up 648 three digit numbers without repetition

It's a two digit number less than 45. It's a prime number. The sum of the numbers is 7, and the difference is 1. What's the number?
A two digit number less than 45 is a prime number with a sum of 7 and a difference of 1

Let the ten bits of this number be x, and the individual bits be y
According to the meaning of the title:
10*x+y

How many three digits can be made up of three digits? Four digits and five digits? What rules do you find? Six, seven and eight digits?