Решение задачи N2598 теория вероятностей

2598. At one factory, for every 100 light bulbs there are on average 10 non-standard ones, on the second - 15, and on the third - 20. The production of these plants makes up respectively 50, 30 and 20% of all light bulbs purchased by residents of the district. Find the probability that:
1) the acquired light bulb is standard;
2) and made the second plant.

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