1.

Bag contains 10 white and 3 black balls.Balls are drawn one by one without replacement till all the black balls are drawn. Find the probability that all black balls are drawn by the 6thdraw.

Answer»

Total no: of balls = 13

probablity of DRAWING a white ball in 1ST draw is 10/13

white ball in the 2nd draw is 9/12

white ball in the 3rd draw is 8/11

a black ball in 4th draw is 3/10

a black ball in the 5th draw is 2/9

a black ball in the 6th draw is 1/8

Therefore the REQUIRED probablity is 10/13 x 9/12 x 8/11 x 3/10 x 2/9 x 1/8 = 4320/1235520 = 432/123552



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