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Probability test question

  1. Feb 9, 2010 #1
    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?
     
  2. jcsd
  3. Feb 9, 2010 #2

    Mark44

    Staff: Mentor

    I don't think you need that part you are subtracting.
     
  4. Feb 9, 2010 #3
    Yeah, I just realized that. The events P(A and 'not B') and P('not A' and B) are mutually exclusive.

    The question was out of 6, so at least I'll get part marks.
     
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