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    Probability




    Hello to everyone...

    I'm very new to stats and have worked through my assignments but am not sure I'm on the right track.

    The question is: Two events, A and B are equally likely. The chance that either A or B happens on a given trial of an experiemtn is 0.70, while the chance that they both happen on a given trial is only 0.40 What is the probability that event A happens?

    I know this is probably pretty basic for you all and I am not looking for help with homework...I'm just really new to stats and am finding some of the concepts pretty difficult.

    Thanks alot...

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    Hi Shannon,

    Welcome to the forum.

    You can use the equation P(A or B) = P(A)+P(B)-P(A and B), since P(A or B) and P(A and B) are given, and P(A)=P(B), it shouldn't be difficult to solve for P(A). Let me know if you have further questions.

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    Thanks very much for your reply and please bear with me. Am I correct then, in determining that A would be the result of P(A or B) - P(A and B) or .30?

    I had determined that I should use the addition equation - as you noted below - and although I know this is relatively simple for the experienced person, I'm having a bit of a time with it.

    Thanks again and I appreciate your help...I'm hoping to be able to continue on my own once I'm able to wrap my brain around this concept.

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    Shannon,

    Just substitute the numbers into the formula:

    0.70 = P(A)+P(B)-0.40

    0.70 = P(A)+P(A)-0.40 since P(A)=P(B),

    and solve for P(A).

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    Thanks alot for your help...much appreciated! Shannon

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    You are welcome!

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