Решение задачи N3468 теория вероятностей

3468. At the exam, the student is offered 25 tickets, each ticket has 3 questions. Of the 75 questions included in the tickets, the student knows 60. What is the probability that a ticket taken by a student will contain only one unknown question?

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