The chance of defective screws in three boxes `A ,B ,Ca r e1//5,1//6,1//7,` respectively. A box is selected at random and a screw draw in from it at random is found to be defective. Then find the probability that it came from box `Adot`

The chance of defective screws in three boxes A,B, Care 1/5,1/6,1/7, respectively.A box is selected at random and a screw draw in from it at random is found to be defective. Then find the probability to be defective. A.

There are N+1 identical boxes each containing N wall clocks.r^(th) box contains (r-1) defective and (N-r+1) effective clocks for 1<=r<=N+1. A box is selected at random and from this box a clock is chosen at random and is found to be effective,the probability that it is from km box is (2N2k+lambda)/(N^(2)+N) then find lambda .

(for explantion of Baye's rule ) three boxes contain 6 red , 4 black , 5 red , 5 black and 4 red , 6 black balls repectively one of the box is selected at random and a ball is drawn from it . If the ball drawn is red , find probability that it is drawn from the first bag .

A box contains 90 discs,numbered from 1 to 90. If one disc is drawn at random from the box,find the probability that it bears a prime number <23 .