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Math Help - Couple stat. problems.

  1. #1
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    Couple stat. problems.

    Hi, I just started a stat. class and I'm not quite sure how to do these two homework problems. Any help would be appreciated...thanks!

    Problem 1: A probability distrubtion is partially given in the following table with the additional information that the even values of random variable X are equally likely to occur:

    x -------P(X=x)
    ---------------
    1--------0.20
    ---------------
    2-----------?
    ---------------
    3--------0.20
    ---------------
    4-----------?
    ---------------
    5--------0.30
    ---------------
    6-----------?

    Find the missing probabilities in the above distribution.

    Problem 2: Given below is a summary for the midterm grades of a general physics course.
    n=40
    sample mean=74
    Q1=63
    Q2=76
    Q3=84

    At most, _____ students scored below 63.

    I have any exam coming up and I know there will be two problems similar to these, so feel free to be as detailed as possible! Thanks again!
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by Jimmy23
    Hi, I just started a stat. class and I'm not quite sure how to do these two homework problems. Any help would be appreciated...thanks!

    Problem 1: A probability distrubtion is partially given in the following table with the additional information that the even values of random variable X are equally likely to occur:

    x -------P(X=x)
    ---------------
    1--------0.20
    ---------------
    2-----------?
    ---------------
    3--------0.20
    ---------------
    4-----------?
    ---------------
    5--------0.30
    ---------------
    6-----------?

    Find the missing probabilities in the above distribution.
    The probability of some outcome (the set of all possible outcomes) must be 1
    (that is something must happen). The outcomes: 1, 3, 7 account for a
    total probability of 0.7. This leaves a total probability of 0.3 for the three
    remaining outcomes which we are told are equally likley so each of them has
    a probability of 0.1.

    RonL
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  3. #3
    Grand Panjandrum
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    Quote Originally Posted by Jimmy23
    Problem 2: Given below is a summary for the midterm grades of a general physics course.
    n=40
    sample mean=74
    Q1=63
    Q2=76
    Q3=84

    At most, _____ students scored below 63.
    Q1, Q2 and Q3 denote the quartiles of the course grades. This means that
    25% (or 0.25=1/4) of grades were below 63, 50% were below 75 and 75%
    were below 84.

    So at most 10 students scored below 63.

    RonL
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  4. #4
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    Thanks alot. I originally thought that the answer was 0.1, but I'm always second guessing myself. Guess I should just trust my answers sometimes. Thanks again!
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