3834. There are three batches of light bulbs of 20, 30 and 50 pieces each. The probability that these lights will work for a given time is equal for each batch, respectively, 0.7; 0.8; 0.9. What is the probability that a light bulb out of 100 available will work at random for a given time.

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