2597. At the first plant, for every 100 light bulbs, an average of 90 standard ones are made, on the second - 95, on the third - 85, and their products are respectively 50%, 30%, 20% of all light bulbs supplied to stores in the area. Find the probability of acquiring a standard light bulb.

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