4078. Of the 1000 lamps, 620 belongs to the 1st installment, 190 to the 2nd and the rest to the 3rd installment. In the first batch of 6%, in the second 5%, in the third 4% of defective lamps. One lamp is selected at random. Determine the probability that the selected lamp is defective.

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