3949. Electric bulbs are manufactured at three plants. The first produces 45% of the total number of light bulbs entering the store, the second 40% and the third 15%. The production of the first plant contains 90% of standard lamps, the second - 80%, and the third - 95%. Find the probability that the lamp purchased in the store will be standard.

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