Решение задачи N2993 теория вероятностей

2993. The group brought 30 manuals in mathematics, including 20 in mathematical analysis and 10 in probability theory. A student randomly takes 2 manuals. Find the probability that: a) both manuals will be on the theory of probability, b) at least one will be on the theory of probability.

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