Results 1 to 5 of 5

Math Help - Probability Problem

  1. #1
    Junior Member
    Joined
    Feb 2009
    Posts
    34

    Probability Problem

    A bag contains 4 green balls, 7 red balls and 8 blue balls. Two balls are picked out at random. Find the probability that one green ball and one red ball are picked:

    a) If the two balls were chosen simultaneously;

    b) If the first ball was replaced before the second ball was picked.

    Answer to 4 decimal places.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Sep 2008
    From
    West Malaysia
    Posts
    1,261
    Quote Originally Posted by mr_motivator View Post
    A bag contains 4 green balls, 7 red balls and 8 blue balls. Two balls are picked out at random. Find the probability that one green ball and one red ball are picked:

    a) If the two balls were chosen simultaneously;

    b) If the first ball was replaced before the second ball was picked.

    Answer to 4 decimal places.

    sorry , my mistake ..
    Last edited by mathaddict; March 14th 2009 at 11:48 PM. Reason: mistake
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Feb 2009
    Posts
    34
    Quote Originally Posted by mathaddict View Post
    (a) 4/19x7/18

    (b) 4/19x7/19

    I don't think this is the correct method.... any other suggestions?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by mr_motivator View Post
    I don't think this is the correct method.... any other suggestions?
    Draw a tree diagram.

    (a) \left( \frac{4}{19}\right) \cdot \left( \frac{7}{18}\right) + \left( \frac{7}{19}\right) \cdot \left( \frac{4}{18}\right) = \, ....


    (b) \left( \frac{4}{19}\right) \cdot \left( \frac{7}{19}\right) + \left( \frac{7}{19}\right) \cdot \left( \frac{4}{19}\right) = 2 \left( \frac{4}{19}\right) \cdot \left( \frac{7}{19}\right) = \, ....
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor matheagle's Avatar
    Joined
    Feb 2009
    Posts
    2,763
    Thanks
    5
    The first one is a hypergeometric...

    {{4\choose 1}{7\choose 1}{8\choose 0}\over {19\choose 2}} ={(4)(7)(1)\over (19)(18)/2}\approx .16374269.

    The second is a trinomial...

    {2\choose 1,1,0}\biggl({4\over 19}\biggr)^1\biggl({7\over 19}\biggr)^1\biggl({8\over 19}\biggr)^0 ={2\over (1)(1)(1)}\biggl({4\over 19}\biggr)\biggl({7\over 19}\biggr)\approx .155124654.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Probability problem
    Posted in the Statistics Forum
    Replies: 4
    Last Post: January 30th 2011, 07:16 PM
  2. Replies: 10
    Last Post: January 21st 2011, 11:47 AM
  3. Probability problem
    Posted in the Statistics Forum
    Replies: 2
    Last Post: October 30th 2009, 02:40 PM
  4. Replies: 0
    Last Post: October 8th 2009, 08:45 AM
  5. probability problem
    Posted in the Statistics Forum
    Replies: 2
    Last Post: August 16th 2008, 12:45 PM

Search Tags


/mathhelpforum @mathhelpforum