Решение задачи N5323 теория вероятностей

5323. From a batch in which 31 parts are free of defects and six are defective, three parts are taken at random. What is the probability that:
a) all three parts without defect;
b) at least one item without a defect?

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