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Math Help - Probability with Z

  1. #1
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    Probability with Z

    Having problem with two questions in a test.

    Question 1

    Suppose that Z is a standard normal random variable. Find P(Z < 1.2). Round to two decimals, for example 0.34

    I have tried 0,89 and 1-0.89=0,1152 = 0,12.

    Question 2

    Z is a standard normal random variable. Find z such that P(-z < Z < z) = 0.5. Round to two decimals

    I have tried 0.00 och 0.69 without sucess

    Thanks
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  2. #2
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    ditt svar till fråga 1 är 0.88

    och till fråga 2 är 0.67

    fråga 3 är alternativ 3&5 om du inte redan klurat ut det.



    kul att du också läser nek B på distans! Vi kanske kan hjälpa varandra här i fortsättningen?
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  3. #3
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    If z is a "standard" normal random variable, that means whatever its mean was, it has been standardized to ZERO, and thus the z-score table for the normal distribution is what you are meant to use here. Therefore the probability thatZ is less than 1.2 is equal to the cummulative probability at z = 1.2 on a z-score chart.

    For the second one, you are told that the probability between -z, and z is 0.5. Do you understand what this means? Look at the values of "z"; they are equal correct, in the sense that z is the number of standard deviations away from the mean - -z simply goes to the left of Z, and +z goes to the right of Z. The easiest way to find z's is to fix Z as the mean (theres no way of knowing this because the information you post doesn't give us any indicator). Looking at a normal chart it looks like 0.65 is a good choice for a portion of the graph that is .25 percentage points; since by symmetry the other z needs to have the same amount of its brother - .5/2).
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  4. #4
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    Quote Originally Posted by mysterion View Post
    ditt svar till fråga 1 är 0.88

    och till fråga 2 är 0.67

    fråga 3 är alternativ 3&5 om du inte redan klurat ut det.



    kul att du också läser nek B på distans! Vi kanske kan hjälpa varandra här i fortsättningen?
    Rough translation: your answer to question 1 is 0.88

    and to question 2 is 0.67

    Question 3 is option 3 & 5 if you have not already figured it out.

    fun that you also read nek B at a distance! Maybe we can help each other here in the future?
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  5. #5
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    Here's a graph to help clarify working with the z-tables.
    Attached Thumbnails Attached Thumbnails Probability with Z-z.jpg  
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