3964. Electric bulbs entering the store are manufactured at three plants. The first plant produces 60% of the total number of light bulbs, the second 25% and the third 15%. The production of the first plant contains 85% of standard lamps, the second 90% and the third 70%. 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)