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Probability - Terminology

  1. Sep 22, 2007 #1
    Data gathered at a particular blood center show that 0.1% of all donors test positive for human immunodeficiency virus (HIV), 1% test positive for herpes, and 1.05% test positive for HIV or herpes.

    Does the part in bold mean the union of HIV and herpes?
     
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  3. Sep 22, 2007 #2

    HallsofIvy

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    Yes "A or B" means in set A or in set B and, yes, that is the union. Notice that the value for "HIV or Herpes" is slightly LARGER than for herpes only.
    In general, P(A or B)= P(A)+ P(B)- P(A and B). Here, since 1.05= 0.1+ 1- 0.05 we can se that the test is 0.5 positive for "Herpes and HIV".
     
  4. Sep 23, 2007 #3

    EnumaElish

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    Halls, I know you meant 0.05 positive for "Herpes and HIV".
     
  5. Sep 23, 2007 #4

    HallsofIvy

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    Thanks. Yes, of course, 0.05.
     
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