Results 1 to 6 of 6

Math Help - subset question

  1. #1
    Junior Member
    Joined
    Nov 2008
    Posts
    50

    subset question

    A⊂(1,2,3......100) |A|=10
    how many subsets posibilities exist that A will be a subset.
    i know the answers is 2^10, but why????
    if A⊂(1,2,3......200) |A|=10, so the number of posebilitis of A been a subset is still 2^10??? why? and how???
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,607
    Thanks
    1574
    Awards
    1
    Quote Originally Posted by tukilala View Post
    A⊂(1,2,3......100) |A|=10
    how many subsets posibilities exist that A will be a subset.
    i know the answers is 2^10, but why???? if A⊂(1,2,3......200) |A|=10, so the number of posebilitis of A been a subset is still 2^10??? why? and how???
    There are indeed 2^{10} subsets of A.
    BUT, that is not the way you have worded the question.
    You have ask “how many subsets of {1,2,3,…,100} are supersets of A
    That is how many subsets of {1,2,3,…,100} have A as a subset.
    The answer to that is 2^{90}. So which is your question?
    Is it about subsets of A? Or is it about supersets of A?
    There is no point in my guessing which question you need help with.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Nov 2008
    Posts
    50
    i ment how many sets with length=10 exist in {1,2,3,....,100}

    for example: (1,2,3,4,5,6,7,8,9,10),(1,2,3,4,5,6,7,8,9,11),(1,1 0,20,30,40,50,60,70,80,90,100),(91,92,93,94,95,96, 97,98,99,100) ,.................................
    so how many? and how are you get to the answer???
    thanks
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,607
    Thanks
    1574
    Awards
    1
    Quote Originally Posted by tukilala View Post
    i ment how many sets with length=10 exist in {1,2,3,....,100}
    That is a simple combination question: {{100}\choose{10}}=\frac{100!}{(10!)(90!)}
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Nov 2008
    Posts
    50
    ok,
    so i want to pick 10 elements of the initial set, which contains 100 elements
    i know that the answer sepose to be 2^10, but why???? i dont understand...
    if i want to pick 10 elements of the initial set, which contains 200 elements, so how many sub set will be now? still 2^10?? if yes, why?
    if not so how many? and why?
    thnx
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,607
    Thanks
    1574
    Awards
    1
    Quote Originally Posted by tukilala View Post
    ok,
    so i want to pick 10 elements of the initial set, which contains 100 elements i know that the answer sepose to be 2^10, but why????
    That statement is simply wrong!
    There are \frac{100!}{(90!)(10!)} ways to pick 10 elements from a set of 100.

    Why do you think there are only 2^{10}? That is the number of subsets in a set of 10.

    There are \frac{200!}{(190!)(10!)} ways to pick 10 elements from a set of 200.

    There are \frac{300!}{(290!)(10!)} ways to pick 10 elements from a set of 300.

    etc
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. pairwise disjoint subset question
    Posted in the Differential Geometry Forum
    Replies: 8
    Last Post: October 12th 2011, 06:34 PM
  2. subset question
    Posted in the Differential Geometry Forum
    Replies: 9
    Last Post: October 4th 2011, 03:05 AM
  3. Measurable Subset Question
    Posted in the Differential Geometry Forum
    Replies: 1
    Last Post: September 27th 2011, 10:24 AM
  4. Proof on Openness of a Subset and a Function of This Subset
    Posted in the Differential Geometry Forum
    Replies: 3
    Last Post: October 24th 2010, 09:04 PM
  5. Connected subset of a Topology Question
    Posted in the Differential Geometry Forum
    Replies: 1
    Last Post: April 8th 2009, 09:16 PM

Search Tags


/mathhelpforum @mathhelpforum