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Math Help - Distribution

  1. #1
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    Distribution

    Dear reader,

    I need help with a problem which I can not solve. I hope you can help me.

    Question:
    The time needed to complete a final examination in statistics course is normally
    distributed with a mean of 80 minutes and a standard deviation of 10 minutes.

    Answer the following questions.

    a) What is the probability of completing the exam in one hour or less?

    b) What is the probability that a student will complete the exam in more than 60
    minutes but less than 75 minutes?

    c) Assume that the class has 60 students and that the examination period is 90
    minutes in length. Find the probability that 60 randomly selected students
    will have a mean time to complete the exam greater than 90 minutes.
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  2. #2
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    Re: Distribution

    If someone can explain the answer for the first question only it would be perfect.
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  3. #3
    MHF Contributor matheagle's Avatar
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    Re: Distribution

    P(X<60)=P\left({X-\mu\over\sigma}<{60-80\over10\right)=P(Z<-2)\approx .0228
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  4. #4
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    Re: Distribution

    Ok, I understand the formula. But how do u come on the answer: 0.0228
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  5. #5
    MHF Contributor matheagle's Avatar
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    Re: Distribution

    I am sure your book has a st normal table and that your professor covered that.
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