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Homework Help: Conditional Probabilities problem

  1. Oct 31, 2011 #1
    1. The problem statement, all variables and given/known data ******* SOLVED *********

    There are three magazines A,B and C respectively. A survey of readers was taken and the following data was collected.

    0.6 Read A
    0.5 Read B
    0.5 Read C
    0.3 Read A&B
    0.2 Read B&C
    0.3 Read A&C
    0.1 Read A&B&C

    What is the probability that a reader reads two magazines exactly?

    2. Relevant equations

    P(R|Q) = P(Q n R) / P(Q) = probability of R given Q. where R,Q are events.

    3. The attempt at a solution

    I attempted this by just using logic. I thought that readers who read A&B,B&C,A&C but not all three magazines would be the solution: giving a probability of 0.5 which I believe is correct.

    I assume conditional probability is meant to be used in the solution but I am unable to see how the sums fit. Any help would be much appreciated.
    Last edited: Oct 31, 2011
  2. jcsd
  3. Oct 31, 2011 #2


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    Homework Helper

    It is easy to solve by the Venn diagram.

  4. Oct 31, 2011 #3
    thanks ehild, that's pretty much how I did it. I thought there was more to it, I was looking for unicorns and finding donkeys.
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