Solution of problem N2976 probability theory

Solution of problem N2976 probability theory

2976. The first box contains 20 parts, 15 of which are standard; in the second - 30 parts, of which 24 are standard; in the third - 10 parts, of which 6 are standard. Find the probability that at random the extracted part from the randomly taken box is standard.

Additional information:

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