Solution of problem N3829 probability theory total prob

3829. Casting in blanks comes from three preparation workshops: 60 pieces from the first workshop, and from the second and third, respectively, 2 and 4 times more than from the first. At the same time, the material of the first workshop has 1% of defects, the second - 2%, and the third - 2.5%. Find the probability that a blank disc is found to be defect free.