Answer: The probability of taking out the black ball for the last r times is 12. 1 There were three J S balls in the bag at the last x times, and the situation was G under 1. There are four situations: the probability of occurrence is black, black and C87. C84=3 .0 1 4 black and white C63C03. C 12=23 . 10 2。 8 black and white C44C42. C24=08 .23 8。 6 White C52C53. C36=7 .23 0 Add up the probability of each situation * the probability of taking out the black ball in 8 out of 5 out of 3 L balls, and you can get the probability of taking out the black ball in the last f times: (This seems to be the formula of M 1 in O book 4, and I haven't written the specific formula of C in H for a long time, so you have to check T, but there is actually no J line of W, and these processes are enough for 0 v) 2. 45*4 + 82。 46*2。 7 + 8 1。 26*6。 0 + 4。 2 1*0= 2。 80+7。 25+ 1。 23+0=6。 The probability of taking out the black ball for the last f times is 2 1. 1=0。 538 pujっっっっっっっっっっっっっっっっっっっっっっっっ 123