The first question is about the arrangement and combination, which means that ten cars race and two cars race together once. If each car needs to race with every other car twice, how many races does each car need to hold? You can consider each car racing against other cars once, that is, 10*9/2, and then multiply it by 2 to get the total number of two races ~ ~ (if you can't play the combination symbol, just write the algorithm directly). You can review the problem of permutation and combination, but generally there won't be too many such problems.

I don't quite understand the second question at the moment.

The third question is to ask how many times the multiple of 12 is 30 when it is less than or equal to 360. You can calculate my understanding, but I feel that this is not the answer. . )