Results 1 to 3 of 3

Math Help - Permutations and Combinations Help!

  1. #1
    Newbie
    Joined
    Sep 2009
    Posts
    5

    Permutations and Combinations Help!

    Hello, what are some ways/tips that i can use to help me distinguish between permutation and combination word problems?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,649
    Thanks
    1597
    Awards
    1
    Quote Originally Posted by TheCB4 View Post
    Help me distinguish between permutation and combination word problems?
    You ask one question.
    Is this about content or is it about order?
    If it involves order it is a permutation.
    If only content matters then it is a combination.

    How many ways can you make a four-letter string using the letters in S~O~U~T~H~E~R~N?
    That is a permutation.

    How many ways can you select four letters from S~O~U~T~H~E~R~N?
    That is a combination.
    Last edited by Plato; November 25th 2009 at 02:33 PM.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,738
    Thanks
    644
    Hello, TheCB4!

    What are some ways/tips that i can use to help me distinguish
    between permutation and combination word problems?
    In a permutation, the order of the objects is important.


    Suppose there are 10 books on the table
    . . and you may select 4 of them.

    If you choose the 4 books and place them in a row on a shelf,
    . . it is a permutation.

    There are: . _{10}P_4 \:=\:\frac{10!}{6!} \:=\:10\cdot9\cdot8\cdot7 \:=\:5040 possible arrangments.


    If you choose the 4 books and toss them into a shopping bag,
    . . it is a combination.

    There are: . _{10}C_4 \:=\:\frac{10!}{4!\,6!} \:=\:210 possible selections.


    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. combinations and permutations
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: June 1st 2010, 02:49 PM
  2. I need help in Permutations and Combinations
    Posted in the Discrete Math Forum
    Replies: 5
    Last Post: May 23rd 2010, 03:04 PM
  3. combinations of permutations?
    Posted in the Discrete Math Forum
    Replies: 4
    Last Post: November 10th 2009, 06:21 PM
  4. Permutations and Combinations
    Posted in the Statistics Forum
    Replies: 1
    Last Post: May 12th 2008, 10:07 AM
  5. Combinations and permutations
    Posted in the Statistics Forum
    Replies: 2
    Last Post: March 18th 2008, 04:10 PM

Search Tags


/mathhelpforum @mathhelpforum