In mathematical problems, a number consists of nine consecutive natural numbers. Why is it also a multiple of 9?
The sum of each digit of a number is 9, and this number is a multiple of 9. You can set the first digit as X, then the next digits are X+ 1, X+2, X+3, X+4, X+5, X+6, X+7, X+8, which adds up to 9x+36, that is, 9 (.