3836. There are three batches of radio tubes, numbering respectively 10, 40 and 50 pieces. The probabilities that the lamp will last for a given time are equal, respectively, for these batches to 0.6; 0.7 and 0.8. Find the probability that a selected lamp of 100 will work at random for a given time.

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