A kind of dice, first throw 1 ~ 9 points, second throw?

It doesn't matter how many dice are rolled for the first time, there is no probability.

For the second roll of the dice, because the sum of points is required to be 7, no matter what the first roll of the dice is, a unique point must be thrown for the second roll, and the probability of throwing a unique point is 1/6, so the answer to this question is 1/6.

A more troublesome solution:

The arrangement produced by rolling the dice twice is 6*6=36, and the possibility that the sum of points is 7 is:1+6; 2+5; 3+4; 4+3; 5+2; 6+ 1; A ***6 groups, so the probability is 6/36 = 1/6.