Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Probability ( simple q )

  1. Jul 14, 2004 #1
    what does this mean?

    P (A or B but not both ( A and B ) ) ?

    does it mean
    P (A U B ) - P (A intersect B )?
  2. jcsd
  3. Jul 14, 2004 #2
    Yes that is correct. By the way, do you know how to draw "Venn's diagram"? That would make things a bit easier.
  4. Jul 14, 2004 #3
    i ask that question because i see my friend work
    she said it means

    P ( A U B ) - 2 P ( A intersect B )

    and she get the answer.
  5. Jul 14, 2004 #4
    Ok, I think it means P(A)+P(B)-2P(A intersects B).
  6. Jul 14, 2004 #5
    thats it. thanks.
  7. Jul 14, 2004 #6
    I believe your problem is essentially solved but it is helpful to construct Venn diagrams in such situations (as Wong suggested) to make some useful generalizations. Set theoretically, A or B but not not both A and B means that the region in the venn diagram that is common to both A and B is excluded (of course, the region described by the sample space - (A+B) is also excluded). This translates (in the "only" notation) to,

    (A only) \bigcup (B only)

    which really is

    (A \bigcap B') \bigcup (A' \bigcap B)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook