Probability Help

Harpy · 2015-07-19 18:26:03

Hi guys wondering if anyone could help me. the question is suppose A and B are evens from a sample space such that P(A)= 0.65 P(B) = 0.45 and P(AnB) = 0.32 Find P(B\A)... I thought you would use the p(BnA) divided by P(B) so .32/.45 and get an answer of .71 But in the solution they're using a venn diagram and he answer is…

19-07-2015 07:26PM

#1

Harpy

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Hi guys wondering if anyone could help me.
the question is
suppose A and B are evens from a sample space such that
P(A)= 0.65 P(B) = 0.45 and P(AnB) = 0.32

Find P(B\A)...

I thought you would use the p(BnA) divided by P(B) so .32/.45 and get an answer of .71

But in the solution they're using a venn diagram and he answer is .13...

Why are they using a venn diagram and not the formula? and how do i know when im supposed to use that method..

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Comments

#2 20-07-2015 02:05AM

MathsManiac

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P(B\A) is the probability of "B less A".
P(B|A) is the probability of B given A.
They are not the same thing.
The question asked for the first and you found the second.

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#3 20-07-2015 05:17PM

Harpy

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Thank you..

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