Results 1 to 2 of 2

Math Help - Trouble understanding combinations

  1. #1
    Junior Member
    Joined
    Jan 2010
    Posts
    43

    Exclamation Trouble understanding combinations

    I'm having trouble understanding this, any explaination or info would be great.

    Jane calculated 10C2 to be 45 arangements. she then calculated 10C8 to be 45 arrangements
    A.) explain in words why 10C2=10C8
    B.) prove the identity nCr= nCn-r
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Mar 2008
    Posts
    934
    Thanks
    33
    Awards
    1
    Quote Originally Posted by nightrider456 View Post
    I'm having trouble understanding this, any explaination or info would be great.

    Jane calculated 10C2 to be 45 arangements. she then calculated 10C8 to be 45 arrangements
    A.) explain in words why 10C2=10C8
    B.) prove the identity nCr= nCn-r
    Suppose you have 10 shirts, all different. When you take 2 shirts out of your closet, you are leaving 8 shirts behind. If you know the 8 shirts left behind, you have uniquely identified the 2 you took out; and if you know the 2 you took out, you know exactly which set of 8 you left behind. So there are exactly as many ways to take out 2 shirts as there are ways to to leave 8 behind.

    Put more abstractly, there is a one-to-one correspondence between subsets of size 2 taken from a set of size 10 and subsets of size 8 taken from the same set.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] Trouble understanding Subspaces
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: September 30th 2010, 12:37 AM
  2. Having some trouble understanding ideals...help?
    Posted in the Advanced Algebra Forum
    Replies: 0
    Last Post: April 27th 2010, 06:38 PM
  3. trouble understanding free varibles
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: September 16th 2009, 07:24 AM
  4. Replies: 3
    Last Post: April 11th 2009, 05:06 PM
  5. Having trouble understanding this example
    Posted in the Trigonometry Forum
    Replies: 5
    Last Post: March 21st 2009, 12:33 AM

Search Tags


/mathhelpforum @mathhelpforum