Results 1 to 4 of 4

Math Help - what is the chance of this happening

  1. #1
    Member Jskid's Avatar
    Joined
    Jul 2010
    Posts
    160

    [RESOLVED]what is the chance of this happening

    I'm stuck on this question
    Suppose that 40% of visitors to a city visit the mountains, 70% visit the parks and 20% visit both sites. One visitor is randomly slected. What is the probability that the visitor visits at least 1 of the 2 sites?

    I tried adding 40%+70%+20% but that's more than 100%
    Last edited by Jskid; July 10th 2010 at 06:54 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor undefined's Avatar
    Joined
    Mar 2010
    From
    Chicago
    Posts
    2,340
    Awards
    1
    Quote Originally Posted by Jskid View Post
    I'm stuck on this question
    Suppose that 40% of visitors to a city visit the mountains, 70% visit the parks and 20% visit both sites. One visitor is randomly slected. What is the probability that the visitor visits at least 1 of the 2 sites?

    I tried adding 40%+70%+20% but that's more than 100%
    Think in terms of sets/Venn diagrams...
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member Jskid's Avatar
    Joined
    Jul 2010
    Posts
    160
    Is it 40%+70%-20% because the overlapping portion is allready counted in the 40% and 70%?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor undefined's Avatar
    Joined
    Mar 2010
    From
    Chicago
    Posts
    2,340
    Awards
    1
    Quote Originally Posted by Jskid View Post
    Is it 40%+70%-20% because the overlapping portion is allready counted in the 40% and 70%?
    Yes. What you did was count first with duplicates, and then subtract the duplicates to get the correct answer. (Well done!) Another (longer) way to think of it is:

    40% visit mountains
    70% visit parks
    20% visit both

    If 40% visit mountains and 20% visit both, then 20% visit ONLY mountains.

    If 70% visit parks and 20% visit both, then 50% visit ONLY parks.

    So (only mountains) + (both mountains and parks) + (only parks) = 20% + 20% + 50% = 90%.

    By the way, the way you dealt with duplicates is a special case of the more general inclusion–exclusion principle.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. prob of not happening
    Posted in the Statistics Forum
    Replies: 2
    Last Post: July 26th 2010, 01:00 PM
  2. Proof question: What's happening?
    Posted in the Differential Geometry Forum
    Replies: 1
    Last Post: January 15th 2010, 02:22 PM
  3. Inequalities - What is happening here?
    Posted in the Algebra Forum
    Replies: 4
    Last Post: December 8th 2009, 01:34 PM
  4. how is this happening?
    Posted in the Calculus Forum
    Replies: 2
    Last Post: March 25th 2009, 09:39 AM
  5. Probability of same event happening in a row
    Posted in the Advanced Algebra Forum
    Replies: 4
    Last Post: June 4th 2008, 01:33 PM

Search Tags


/mathhelpforum @mathhelpforum