Results 1 to 6 of 6

Math Help - permutation question

  1. #1
    Member
    Joined
    Oct 2007
    Posts
    159

    permutation question

    If you have a five bit string ABCDE, how many strings can you make that have A before C and C before E?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,969
    Thanks
    1788
    Awards
    1
    Quote Originally Posted by Frostking View Post
    If you have a five bit string ABCDE, how many strings can you make that have A before C and C before E?
    In any rearrangement of “ABCDE” we can leave the B & D fixed rearrange the A, C & E is six ways. But only one of those do A, C & E appear in that order. So the answer is one-sixth of the total.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Oct 2007
    Posts
    159

    reply to permutation question

    So, you are saying since there are 120 total ways to arrange a five bit string with ABCDE, there would be 20 of these in which A is before C and C is before E? Can I then think of it as choosing the other two members D and B in 5 x 4 ways? Or is that in error? Thanks so much for your prompt help!
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Apr 2008
    Posts
    11
    since there got 5 string, let this to be 5 empty space
    _ _ _ _ _
    given situation some thing look like A->C->E (A before C before E)
    from this 5 empty space, choose 3 of this 5, therefore there have C(5,3)=10
    ways to put A C E, this left B and D, after finish put A C E, there left 2 free space for B and D. Hence C(5,3)*2*1=20
    Last edited by lekge; April 11th 2008 at 07:44 AM.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,914
    Thanks
    779
    Hello, Frostking!

    If you have a five bit string ABCDE, how many strings can you make
    that have A before C and C before E?

    Since A, C, E will appear in alphabetical order,
    . . the only issue is the placement of B and D.

    And there are:. P(5,2) \:=\:20 ways.

    Follow Math Help Forum on Facebook and Google+

  6. #6
    Member
    Joined
    Oct 2007
    Posts
    159

    Permutation question help

    Thank you Soroban and Lekge for adding your explanations. I really appreciate the help!!!!!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. permutation question
    Posted in the Discrete Math Forum
    Replies: 1
    Last Post: February 20th 2011, 08:48 AM
  2. Another Permutation question
    Posted in the Statistics Forum
    Replies: 2
    Last Post: December 6th 2010, 07:12 PM
  3. permutation question
    Posted in the Statistics Forum
    Replies: 4
    Last Post: June 1st 2009, 05:16 PM
  4. Permutation Question
    Posted in the Discrete Math Forum
    Replies: 4
    Last Post: March 30th 2009, 01:13 PM
  5. question on permutation
    Posted in the Statistics Forum
    Replies: 4
    Last Post: October 27th 2006, 06:47 PM

Search Tags


/mathhelpforum @mathhelpforum