1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Independent event does not seem to follow rule

  1. Apr 18, 2012 #1
    Hello. I'm trying to understand why P(A|B) ≠ (PA) given that the events are indepent is this case. I am not sure if my working out is correct but the answer is 1/8 in the answer section.

    Events A and B are defined in the sample space S. The events A and B are independent.
    P(A) = 0.3, P(B) = 0.4 and P(A U B) = 0.65.

    Find P(A|B).


    3. The attempt at a solution:
    P(A n B) = P(A) + P(B) - P(A U B)
    P(A n B) = 0.3 + 0.4 - 0.65 = 0.05

    P(A|B) = P(A n B) / P(B)
    P(A|B) = 0.05 / 0.4
    P(A|B) = 1 / 8
     
  2. jcsd
  3. Apr 18, 2012 #2

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    There is something wrong with the problem statement. From P(A)=0.3, P(B)=0.4 and P(A or B) =0.65, it follows that P(A & B) = 0.05, just as you have said. However, P(A)*P(B) = 0.12, which is ≠ P(A & B), so A and B cannot be independent.

    RGV
     
    Last edited: Apr 18, 2012
  4. Apr 18, 2012 #3
    Thank you. Must be an error I'm guessing.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Independent event does not seem to follow rule
  1. Independent events (Replies: 3)

Loading...