Решение задачи N4632 теория вероятностей

4632. The student knows 15 out of 25 questions. He is asked 3 questions in sequence. What is the probability of events:
a) the student will answer the first question, but not the second and third;
b) the student will answer only one question;
c) the student will answer at least one question;
d) answer two questions;
e) does not answer at least one question;
e) does not answer all questions.

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