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s1: probability stuck on question Watch

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    Hi, I'm not struggling with a question from my textbook, the answer is P(B=0.5 which works but I don't know how to get it

    The only way I could think about doing it would be trial and error which obviously isn't going to get me a good answer!

    I was thinking you could do 0.6xP(B) + 0.4xP(B) + 0.6xP(B') =0.7 but that wouldn't work would it as how can we assume P(B)=P(B')?
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    (Original post by Jitesh)
    Hi, I'm not struggling with a question from my textbook, the answer is P(B=0.5 which works but I don't know how to get it

    The only way I could think about doing it would be trial and error which obviously isn't going to get me a good answer!

    I was thinking you could do 0.6xP(B) + 0.4xP(B) + 0.6xP(B') =0.7 but that wouldn't work would it as how can we assume P(B)=P(B')?
    I'm assuming this is Q12:

    Use the formula : P(\text{A or B or both}) = P(A) + P(B) - P(\text{A and B})

    Usually written with symbols : P(A\cup B) = P(A) + P(B) - P(A \cap B)


    Also, since A and B are independent you have the formula

    P(\text{A and B}) = P(A) \times P(B)
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    (Original post by notnek)
    I'm assuming this is Q12:

    Use the formula : P(\text{A or B or both}) = P(A) + P(B) - P(\text{A and B})

    Usually written with symbols : P(A\cup B) = P(A) + P(B) - P(A \cap B)


    Also, since A and B are independent you have the formula

    P(\text{A and B}) = P(A) \times P(B)
    Sorry I meant q11, but it seeems like you answered q11?

    Sorry what does the cup mean? and/or ?
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    (Original post by Jitesh)
    Sorry I meant q11, but it seeems like you answered q11?

    Sorry what does the cup mean? and/or ?
    Yes I meant Q11

    \cup = \text{or}

    \cap = \text{and}
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    (Original post by notnek)
    Yes I meant Q11

    \cup = \text{or}

    \cap = \text{and}
    Sorry I'm confused on to how you would get P(AnB) without knowing the value of B?
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    (Original post by Jitesh)
    Sorry I'm confused on to how you would get P(AnB) without knowing the value of B?
    If you combine the first formula with the second formula I gave you:

    P(A\cup B) = P(A) + P(B) - P(A)\times P(B)


    You know P(A\cup B) and P(A) so you can work out P(B).
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    (Original post by notnek)
    If you combine the first formula with the second formula I gave you:

    P(A\cup B) = P(A) + P(B) - P(A)\times P(B)


    You know P(A\cup B) and P(A) so you can work out P(B).
    Oh, that's great! Thank you very much!
 
 
 
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