Solution of problem N3903 probability theory total prob

Solution of problem N3903 probability theory total prob

3903. The collector received 3 boxes of parts: in the first box 40 parts, 20 of them painted; in the second - 50, of which 10 are painted; in the third - 30 parts, 12 of them painted. Find the probability that at random the extracted part from the randomly taken box will be colored.

Additional information:

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