Solution of problem N3922 probability theory total prob

Solution of problem N3922 probability theory total prob

3922. In the batch of mechanisms 50% of the first grade, 40% of the second grade and 10% of the third grade. Marriage among the mechanisms of each class is 2%, 4% and 7% respectively. The mechanism was defective. What is the probability that he is of the first grade?

Additional information:

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