Решение задачи N3465 теория вероятностей

3465. At the exam, the student is offered 30 tickets; Each ticket has two questions. Of the 60 questions included in the tickets, the student knows only 40. Find the probability that the ticket taken by the student will be
1. of the questions known to him;
2. of the unknown issues;
3. from one known and one unknown question.

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