Results 1 to 4 of 4

Math Help - Permutation and combination help!

  1. #1
    Newbie
    Joined
    Oct 2010
    Posts
    4

    Permutation and combination help!

    A box contain 8 balls, of which 3 are identical and the other 5 are different from each other. 3 balls are to be picked out of the box; the order in which they are picked out does not matter. Find the number of different possible selections of 3 balls. can someone solve this question asap? thanks!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor undefined's Avatar
    Joined
    Mar 2010
    From
    Chicago
    Posts
    2,340
    Awards
    1
    Quote Originally Posted by CautionItsHot View Post
    A box contain 8 balls, of which 3 are identical and the other 5 are different from each other. 3 balls are to be picked out of the box; the order in which they are picked out does not matter. Find the number of different possible selections of 3 balls. can someone solve this question asap? thanks!
    What have you tried so far? Please take the time to familiarize yourself with some basic forum rules. This is not a place to get people to do your homework for you.

    http://www.mathhelpforum.com/math-he...ng-151422.html

    That said, rather than finding a more elegant solution that generalizes to harder problems, for this we can simply break down into cases. Suppose the 3 identical balls are identified by the colour green. Four cases: 0 green, ... , 3 green. Then you've reduced it to problems that (supposedly) you already know how to solve.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Oct 2010
    Posts
    4
    case 1: 0 green 3diff =5C3
    case 2: 1 green 2 diff=5C2x3C1
    case 3:2 green 1 diff= 5C1x3C2
    case4: 3 green 0 diff=3C3

    Thats wat i done intinially. i add them up and my ans is 56. but the correct ans is 26. where is it that i have gone wrong
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor undefined's Avatar
    Joined
    Mar 2010
    From
    Chicago
    Posts
    2,340
    Awards
    1
    Quote Originally Posted by CautionItsHot View Post
    case 1: 0 green 3diff =5C3
    case 2: 1 green 2 diff=5C2x3C1
    case 3:2 green 1 diff= 5C1x3C2
    case4: 3 green 0 diff=3C3

    Thats wat i done intinially. i add them up and my ans is 56. but the correct ans is 26. where is it that i have gone wrong
    You are treating the green balls as distinguishable. Note that C(8,3) = 56.

    Corrected work: C(5,0) + C(5,1) + C(5,2) + C(5,3) = 26.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Permutation vs Combination
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: September 26th 2009, 02:18 PM
  2. Permutation/combination?
    Posted in the Statistics Forum
    Replies: 2
    Last Post: March 28th 2009, 08:45 AM
  3. Permutation or Combination?
    Posted in the Statistics Forum
    Replies: 1
    Last Post: November 16th 2008, 10:33 AM
  4. combination/permutation
    Posted in the Discrete Math Forum
    Replies: 0
    Last Post: October 16th 2008, 11:40 PM
  5. Permutation and Combination Help!
    Posted in the Statistics Forum
    Replies: 6
    Last Post: March 18th 2008, 12:21 PM

Search Tags


/mathhelpforum @mathhelpforum