Решение задачи N3398 теория вероятностей

3398. The student came to the test, knowing only 30 out of 30 questions. The teacher asks three questions. The test will be handed over if the student answers at least two of the three questions. What is the probability that this student will pass the test.

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