4021. The shop receives the same type of products from three plants, with the i-th (i = 1,2,3) plant supplying mi percent of the products (40%, 20%, 40%). Among the products of the i-th plant, ni percent are first-rate (90%, 90%, 80%). Bought one product. It turned out to be first-rate. Determine the probability that the purchased product is produced by the 2nd plant.

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