Something's wrong! I.e. the elimination sequence.

In the simplest way, ten people line up, and only the order of A, B and C in the team must be from left to right (but people can be inserted).

The answer is 10! Divide by 3!

10! It refers to the possibility of all sequences produced by the arrangement of the whole person, but in the topic, the order of the three people has been decided in advance, so it is not necessary to arrange them all, but 10! Arrange them together when arranging, so we need to eliminate the local arrangement order between them, that is, divide by 3!

The final result is similar to the arrangement of ten people, but the three people have a clear order.