September 30 Lecture

# September 30 Lecture - Lecture Section 3.3 Probability...

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Lecture September 30, 2011

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Section 3.3 Probability Rules
Basic Rules For some event, E: 1. 0 Pr{E} 1 2. The sum of the probabilities of all possible events is 1, or Pr{S} = 1 = 3. 1 Pr {} k i i E =

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Rule of Addition ± The events A and B are called mutually exclusive if they cannot occur simultaneously, so P(A and B) = 0. ( ) () a n d ) . PA o r B PB B = +− For any two events A and B, ± If A and B have no points in common, then the above formula becomes ) ( ) ( ) ( B P A P B or A P + =
Example • At a small college, the probability that a student takes physics and sociology is 0.092. The probability that a student takes sociology is 0.73. • Find the probability that the student is not taking sociology. This equals 1 – Pr(student doesn’t take sociology), or 0.27. Complementary Events As noted before in our list of probability rules, for any event, A, Pr(A) = 1 – Pr(A c )

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Clicker Question Which of the following is correct? A) A and B represents an intersection B) A or B means A or B or both C) A c means not in A D) A or B is the union of A and B E) All of the above
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September 30 Lecture - Lecture Section 3.3 Probability...

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