Results 1 to 3 of 3

Math Help - Probability test question

  1. #1
    Member
    Joined
    Oct 2009
    Posts
    114
    Thanks
    1

    Probability test question

    I had this question on a test:

    The probability of snowing in one city is 0.4, and the probability of snowing in another city is 0.7. Assume independence. What is the probability that it snows in exactly one of the two cities?

    The way I approached it was to say that the probability that it snows in exactly one of the two cities is:

    Let A denote probability of snow in the first city.
    Let B denote probability of snow in the second city.

    P(A and 'not B') or P('not A' and B) = (0.4)(0.3) + (0.6)(0.7) - (0.4)(0.3)(0.6)(0.7) = 0.4896

    Is this correct?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Apr 2008
    Posts
    1,092
    There are four possibilities:

    It snows in neither city

    P1 = (0.6)(0.3)

    It snows in both cities

    P2 = (0.4)(0.7)

    It snows in the first city only

    P3 = (0.4)(0.3)

    It snows in the second city only

    P4 = (0.6)(0.7)

    The probability that it snows in exactly one city is simply P3 + P4.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,669
    Thanks
    1618
    Awards
    1
    Quote Originally Posted by BrownianMan View Post
    The probability of snowing in one city is 0.4, and the probability of snowing in another city is 0.7. Assume independence. What is the probability that it snows in exactly one of the two cities?
    Let A denote probability of snow in the first city.
    Let B denote probability of snow in the second city.
    P(A and 'not B') or P('not A' and B) = (0.4)(0.3) + (0.6)(0.7) - (0.4)(0.3)(0.6)(0.7) = 0.4896

    Is this correct?
    No the part in red is not correct.
    Think about it. Can A and notA both happen?
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: May 21st 2010, 09:56 AM
  2. Probability test Question
    Posted in the Statistics Forum
    Replies: 1
    Last Post: December 16th 2009, 07:07 PM
  3. Probability of HIV test
    Posted in the Statistics Forum
    Replies: 1
    Last Post: September 17th 2009, 03:04 AM
  4. Replies: 2
    Last Post: August 27th 2009, 06:54 PM
  5. Probability Test
    Posted in the Statistics Forum
    Replies: 10
    Last Post: April 25th 2008, 12:01 PM

Search Tags


/mathhelpforum @mathhelpforum