3953. Electric bulbs entering the store are manufactured at 3 plants. The first plant produces 20% of the total number of light bulbs, the second 55% and the third 25%. The products of the first one contain 95% of standard lamps, the second one 80% and the third one 90%. What is the probability that a lamp purchased in the store is standard?

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