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    When we have p(A n B) (probability of A intersection B), in what cases can I simply multiply p(A) and p(B) to work this out and when can I not?

    In the cases where I can't use multiplication how do I then go about working it out?

    I ask because I was doing a question and to work out all the intersection I multiplied the probabilities however most of it was incorrect and I had to manually think about which cards were included in the intersection and divide by 52. (question is attached).Name:  Screen Shot 2014-12-28 at 17.59.58.png
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    Can multiply if they are independent. Otherwise have to work out manually each case unless you are given something extra , like P(A|B) and P(B) which becomes obvious how to find intersection.
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    (Original post by hassassin04)
    Can multiply if they are independent. Otherwise have to work out manually each case unless you are given something extra , like P(A|B) and P(B) which becomes obvious how to find intersection.
    So in the attached question was it incorrect to multiply together?
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    (Original post by Davelittle)
    So in the attached question was it incorrect to multiply together?
    I would model this as a Venn diagram (with data rather than probabilities) with 3 overlapping circles
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    (Original post by Davelittle)
    So in the attached question was it incorrect to multiply together?
    For part ii? Why do you want to multiply them? Just think- which card(s) satisfie all those properties? The probability then should be clear.
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    (Original post by hassassin04)
    For part ii? Why do you want to multiply them? Just think- which card(s) satisfie all those properties? The probability then should be clear.
    No for part i. when using the formula for the union of 3 things
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    (Original post by Davelittle)
    No for part i. when using the formula for the union of 3 things
    Same thing. I would just list all cards that satisfy the requirement.
 
 
 
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