math
posted by kholoud .
we have box,in box 3 white balls,4 red balls,4 black balls..how i choose 2 black balls and 3 red balls successively?

chance of picking 1 black first = 4/11
now have 3 w , 4 r , 3 b or 10
chance of picking black second = 3/10
now have 3 w ,4 r, 2 b or 9
chance of picking red = 4/9
now have 3 w, 3 r , 2 b or 8
chance of picking red = 3/8
now have 3 w , 2 r , 2 b or 7
chance of picking res = 2/7
so
4/11 * 3/10 * 4/9 * 3/8 * 2/7