Решение задачи N5117 теория вероятностей

5117. In a lot of 70 identically packaged articles, articles of two grades are mixed, 45 of these articles are of the first class, and the rest of the articles of the second class. 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)