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    We have events A and B

    P(A)= 1/5 and thus P(A')= 4/5

    P(B¦A)= 1/4

    P(B¦A')= 3/8

    How do I find P(B)?


    ps. Sorry for the weird notation on the B given that it's A/A'... Couldn't find the vertical line on my keyboard!
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    (Original post by lalilou)
    We have events A and B

    P(A)= 1/5 and thus P(A')= 4/5

    P(B¦A)= 1/4

    P(B¦A')= 3/8

    How do I find P(B)?


    ps. Sorry for the weird notation on the B given that it's A/A'... Couldn't find the vertical line on my keyboard!
    | is to the left of Z on your keyboard, probably.

    Using the standard formula for conditional probablity, apply it to P(B|A), and see what you can work out. Similarly for the other one.

    For the last step, if you can't think of it, look in the spoiler

    Spoiler:
    Show


    P(B) = P(BnA) + P(BnA')

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    I think this is the way to do it:
    P(B) = [P(B) and P(A) ] divided by the P(A)
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    (Original post by ghostwalker)
    | is to the left of Z on your keyboard, probably.

    Using the standard formula for conditional probablity, apply it to P(B|A), and see what you can work out. Similarly for the other one.

    For the last step, if you can't think of it, look in the spoiler

    Spoiler:
    Show


    P(B) = P(BnA) + P(BnA')

    Thank you!! Ironically, just as I posted the thread, I looked down at my diagram and realised how simple it actually was. Now I feel silly for posting!
 
 
 
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