This question is not reasonable, my understanding is:

From 1 to 9 numbers, select any number in 1 and select it twice in succession. The probability of extracting duplicate numbers twice is 1 1%.

The four numbers of 1 to 9 are selected twice in a row. What is the probability of extracting them twice? %

Ideas:

First of all, 1-9 has 1 = 9 cases when choosing1number, the second case is 9c 1 = 9 cases, and the repeated cases are 1 1, 22,33 .. 99 *.

It can also be understood that there are 9 cases in the first time, 1 case is optional, and only 1 case is repeated in the second time, so the probability is 1/9.

But in the case of four out of nine numbers, * * * is 9C4= 126, 1 optional. If it is repeated for the second time, it will only correspond to 1, so the probability is1126.