Решение задачи N5121 теория вероятностей

5121. In a batch of 31 identically packaged articles, articles of two grades are mixed, 14 of which are Class I and the remainder are Class II. Find the probability that two products taken at random will be: a) of the same sort; b) different varieties.

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