3833. There are 4 batches of lamps of 10, 20, 30 and 40 pieces each. The probability that the lamps will work for a given time is equal for each batch of 0.6, 0.7, 0.8 and 0.9, respectively. What is the probability that a lamp of 100 given lamps selected at random will work for a given time?

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