Results 1 to 3 of 3

Math Help - looking for clarification on a simple argument

  1. #1
    Newbie sonictech's Avatar
    Joined
    Apr 2008
    Posts
    6

    looking for clarification on a simple argument

    So I'm sure anyone who likes probability and statistics enough has heard of this type of question. It goes something along the lines of:

    A mother takes her son, out of two kids, to the park. What is the probability her other child is a girl?

    And I would say 2/3. Because the 4 possible ways of having 2 kids are BB GG BG and GB. So the option GG is eliminated, and of the remaining 3 options another boy occurs once, a girl occurs twice.

    Now on the flip side... if the question said:

    A mother takes her oldest son, out of two kids, to the park. What is the probability her other child is a girl?

    Again... the four possibilities are BB, BG GB and GG. Is birth order relevant to this question? Would the answer still be 2/3 or would it be 1/2 because the option BG is eliminated from the set (assuming girl is the older child in the option BG)
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by sonictech View Post
    So I'm sure anyone who likes probability and statistics enough has heard of this type of question. It goes something along the lines of:

    A mother takes her son, out of two kids, to the park. What is the probability her other child is a girl?

    And I would say 2/3. Because the 4 possible ways of having 2 kids are BB GG BG and GB. So the option GG is eliminated, and of the remaining 3 options another boy occurs once, a girl occurs twice.

    Now on the flip side... if the question said:

    A mother takes her oldest son, out of two kids, to the park. What is the probability her other child is a girl?

    Again... the four possibilities are BB, BG GB and GG. Is birth order relevant to this question? Would the answer still be 2/3 or would it be 1/2 because the option BG is eliminated from the set (assuming girl is the older child in the option BG)
    If you're asking a question, then here's the answer:

    The unrestricted sample space is BB, BG, GB, GG where the younger child is first and the older child second. But what you're calculating is a conditional probability viz. Pr(younger child is G | Older child is B).

    Then the restricted sample space is BB, GB.

    So the answer is clearly 1/2.


    For the first part, you're correct:

    You're calculating a conditional probability viz. Pr(One child is G | One child is B).

    Then the restricted sample space is BB, GB, BG.

    So the answer is clearly 2/3.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie sonictech's Avatar
    Joined
    Apr 2008
    Posts
    6
    good, so we're in agreement. Maybe now my friends will get off my back :P

    thanks!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 4
    Last Post: September 3rd 2011, 04:32 AM
  2. Simple Logarithmic Equation Clarification.
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: September 21st 2010, 02:06 AM
  3. Simple linear algebra justification - clarification
    Posted in the Advanced Algebra Forum
    Replies: 4
    Last Post: February 6th 2010, 08:00 PM
  4. simple clarification
    Posted in the Math Topics Forum
    Replies: 3
    Last Post: January 26th 2010, 09:28 PM
  5. Replies: 3
    Last Post: June 26th 2008, 05:39 PM

Search Tags


/mathhelpforum @mathhelpforum