Thread: Two events and a simple question

what the question states :
"Events A and B are such that:
p(A) = 5/12
p(A|notB)=7/12
P(A intersection B ) =1/8 "

Would I be correct if I assume that Not B refers to A ? , so then i can draw a probability tree.

Originally Posted by terence

what the question states :
"Events A and B are such that:
p(A) = 5/12
p(A|notB)=7/12
P(A intersection B ) =1/8 "

Would I be correct if I assume that Not B refers to A ? , so then i can draw a probability tree.

no you cant assume that, not B not always just A, if A union B is the whole space then not B is in A

Most likely "notB" means "event B did not occur"

I would also advise you to draw a Venn diagram for this question.

Originally Posted by terence

what the question states :
"Events A and B are such that:
p(A) = 5/12
p(A|notB)=7/12
P(A intersection B ) =1/8 "
Would I be correct if I assume that Not B refers to A ? , so then i can draw a probability tree.

.
Now .
Thus

Originally Posted by Plato

.
Now .
Thus

The question then asks for :

i) P(B)
ii) P(A|B)
iii) P(B|A)
iv) P(A U B)


P(B|A) is easy since P(A intersection B) / P(A) = 0.3
Had i known P(B) iv) would have been easy as well.

How can P(B) be found.. ?
Well I know this:

where

Originally Posted by terence

The question then asks for :
i) P(B)
ii) P(A|B)
iii) P(B|A)
iv) P(A U B)
How can P(B) be found.. ?
Well I know this:

where

From the given you can find
But which is given.
From which you can find . From which you can find .

From the given you can find

how can you find this ?

the nearest i can get is that

Originally Posted by terence

how can you find this ?

Oh how dumb of me -.-

I should have reasoned that out. Largest problem with probability=> reasoning simple things out.


Thanks @Plato