Senior high school mathematics, statistics, required questions 3 and 10, don't do it by enumeration, how to write it step by step? I wrote it several times, and the second one was mine.
Numbers less than ten digits: the first digit is 1, 8 digits.
The first two, seven,
. . .
8th, 1, ***36.
If it is greater than 37, the first 4, 5, 6, 7, 8***5+4+3+2+ 1= 15.
Two of the first three, 17.
17/36.