Results 1 to 4 of 4

Math Help - Set Theory Problem

  1. #1
    Newbie
    Joined
    Feb 2007
    Posts
    5

    Set Theory Problem

    I'm not sure if I got this right or not:

    Let A = {n is in Z such that n = 5r for some integer r}
    and
    Let B = {m is in Z such that m = 20s for some integer s}

    * Z is the set of all integers

    1) Is A a subset of B?
    2) Is B a subset of A?

    My reasoning:
    1) No (because every time r is odd there is a new value of n in A which does not appear in B)

    2) Yes (because no matter what s is there is a m value in B which matches a n value in A)

    Is my reasoning sound for these? Thanks for the help!
    Last edited by jtc4zH; February 13th 2007 at 12:17 PM. Reason: Small typo
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,386
    Thanks
    1476
    Awards
    1
    They are correct and the reasons work.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,547
    Thanks
    539
    Hello, jtc4zH!

    Thought I'd test out some codes . . .


    Let .A .= .{n ε Z | n = 5r for some r ε Z}
    Let .B .= .{m ε Z | m = 20s for some s ε Z}

    The code of the usual "membership" symbol doesn't work.
    The number is 8712 . . . precede it with &# and follow it with ; (semicolon).

    This fancy ε has code &# 949 ; .without the spaces.


    1) Is A ⊄ B ?
    2) Is B ⊄ A ?

    Neither 8836 (subset) nor 8834 (proper subset) works here.

    The same is true for 8704 (inverted A) and 8707 (backward E)
    . . and 8709 (null set) . . . very disappointing.


    Follow Math Help Forum on Facebook and Google+

  4. #4
    Newbie
    Joined
    Feb 2007
    Posts
    5
    Cool, I will try to use these next time if I remember!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Set theory problem
    Posted in the Discrete Math Forum
    Replies: 3
    Last Post: September 4th 2011, 05:20 PM
  2. a problem about set theory
    Posted in the Discrete Math Forum
    Replies: 5
    Last Post: July 10th 2010, 09:29 AM
  3. Set Theory Problem
    Posted in the Discrete Math Forum
    Replies: 2
    Last Post: May 7th 2010, 07:58 PM
  4. Set theory problem
    Posted in the Math Challenge Problems Forum
    Replies: 4
    Last Post: November 9th 2009, 09:22 PM
  5. Is {} same as {{}} set theory problem
    Posted in the Discrete Math Forum
    Replies: 6
    Last Post: October 13th 2007, 03:25 PM

Search Tags


/mathhelpforum @mathhelpforum