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Math Help - Set theory question

  1. #1
    Junior Member
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    Sep 2009
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    69

    Question Set theory question

    Past data shows that on the average 18% of students in a certain class receive an A, 22% a B, 25% a C, and 35% fail. Suppose that in a class of 25 students 3 students get an A, 5 students a B, 6 students a C, and the rest fails. Find the probability of this event (assume independence of the students’ grades). Find also the probability that 11 or more of the 25 students fail.

    Help please? i drew a triple venn diagram but i keep coming out with impossible probabilities, like negative numbers.
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  2. #2
    Newbie
    Joined
    Sep 2009
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    The way I'm interpreting your first question, it seems like you have the following:

    P(A) = .18
    P(B) = .22
    P(C) = .25
    P(Fail) = .35

    And you want to figure how the probability that 3 A's occur, 5 B's occur, 6 C's occur, and rest fail. Does this help?
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