Решение задачи N5094 теория вероятностей

5094. There are 15 parts in a box, 3 of which are defective. The assembler draws 4 pieces at random. Find the probability that:
a) the extracted parts are of high quality,
b) among the extracted parts, 1 is defective and 3 are of high quality.

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