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Probability Help

  • 19-07-2015 6:26pm
    #1
    Harpy
    Registered Users, Registered Users 2 Posts: 1,892 ✭✭✭


    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..


Comments

  • #2
    MathsManiac
    Registered Users, Registered Users 2 Posts: 1,595 ✭✭✭MathsManiac


    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.


  • #3
    Harpy
    Registered Users, Registered Users 2 Posts: 1,892 ✭✭✭Harpy


    Thank you..


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