3987. The store received 20 refrigerators "Biryusa", 35 refrigerators "Orsk", 4 refrigerators "Minsk". The probability that the refrigerator will not fail during the warranty period is equal to "Biryusa" - 0.8; for Orsk - 0.9; for "Minsk" - 0.95. The buyer bought one fridge. What is the probability that this is the Orsk refrigerator, if it turned out to be reliable?

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