This answer is given in this way, so it needs to be divided by A22. For example, the packet is 3 1 1. It turns out that after picking up three, the other two will be automatically divided into two groups, one at a time. However, if you choose 1 from the other two, it becomes two, which is actually duplicate, so you need to divide by 2.

The first half can be changed:

Just use C (5,3).