3832. There are three batches of lamps of 20, 30, 50 pieces each. The probability that the lamps will work for a given time is equal for each batch, respectively, 0.7; 0.8; 0.9. What is the probability that a lamp chosen at random from a hundred of these lamps will work for a specified time?

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