Решение задачи N2836 теория вероятностей

2836. In a group of 30 students in the test, 6 students were rated “excellent”, 10 students - “good”, 9 - “satisfactory”. What is the probability that all three students brought to the board have unsatisfactory grades.

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