Решение задачи N4680 теория вероятностей

4680. There are products of four grades, and the number of products of each grade is, respectively, 2, 7, 2, 1. For control, 9 products are taken at random. Determine the probability that among them 1 is a first-class item, 5 is a second-grade item, 2 is a third-grade item, and 1 is a fourth-grade item.

Detailed solution. Decorated in Microsoft Word 2003 (Quest decided to use the formula editor)