Решение задачи N3464 теория вероятностей

3464. At the exam, the student is offered 20 tickets, each with three questions. Of the 60 questions included in the tickets, the student knows 50. What is the probability that a ticket taken by a student will consist of two known and one unknown question?

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