Solution of problem N3856 probability theory total prob

3856. The assembler received two boxes of identical parts manufactured by the plant - 1, three boxes by the plant - 2 and five boxes by the plant - 3. The probability that the detail of the 1st plant is standard is 0.95, the 2nd plant is 0.92 and 3 th 0.9. Find that taken at random item will be standard.