Five workers choose two as storekeepers and one as quality inspector, and there are 10 ways to choose from.

If you don't worry about why, you can enumerate all the possibilities and prove that there are exactly 10.

It can also be explained by combination, that is, there are five ways to choose one person and then four ways to choose another person, so 5*4=20 ways to choose.

However, the two choices are in order, not in the order required by the topic, that is, two people are selected at a time. Therefore, if choosing A first and then choosing B is included in those 20 selection methods, then choosing B first and then choosing A is also included, which is considered as the difference among those 20 selection methods. According to the meaning of the question, these recalculation methods need to be removed, that is, divided by 2, so the total * * * is exactly 10.

Combination:

Combination is a mathematical term. Generally speaking, taking m(m≤n) elements from n different elements as a group is called taking out the combination of m elements from n different elements. We call the problem of finding the combination number the combination problem.

Repeated combination is a special combination. You can repeatedly select m elements from n different elements. Synthesizing a group of m elements called n elements regardless of their order is a repeatable combination.