math

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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?

  • math -

    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

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