Solution of problem N3834 probability theory total prob

Solution of problem N3834 probability theory total prob

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.

Additional information:

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