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More Probability problems

  1. Jan 24, 2008 #1
    [tex] P(\text{stop at first light signal}) = 0.4 = P(A) [/tex]

    [tex] P(\text{stop at second light signal}) = 0.5 = P(B) [/tex]

    [tex] P(\text{stop at least one of two signals}) = 0.6 = P(A \cup B) [/tex]

    Then [tex] P(A \cap B) = P(A) + P(B) - P(A \cup B) = 0.3 [/tex]

    [tex] P( \text{first signal but not second}) = P(A \cap B') = 1-0.3 = 0.7 [/tex]

    [tex] P(\text{exactly one signal}) = P(A \cup B) - P(A \cap B) = P(A \Delta B) = 0.3 [/tex]


    Are these correct?
     
  2. jcsd
  3. Jan 25, 2008 #2

    EnumaElish

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    They are; except can you explain P(1st but not 2nd) = 0.7?
     
  4. Jan 25, 2008 #3
    yeah thats incorrect. It should be [tex] P(A \cap B') = P(A) - P(A \cap B) = 0.4-0.3 = 0.1 [/tex]
     
  5. Jan 27, 2008 #4


    Shouldn't it be [tex]P(A \cap B') = P(A) * (1-P(B))[/tex]

    Assuming there independent
     
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