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Math Help - another question

  1. #1
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    another question

    a) Profits (denoted as X) 100 normally distributed mean value of 1.5 mi and a (s.d.) of 120,000.


    Calculate P (X < $1 million)
    Last edited by crashuk; June 1st 2008 at 05:03 AM.
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  2. #2
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    Quote Originally Posted by crashuk View Post
    a) Profits (denoted as X) in an industry consisting of 100 firms are normally distributed with a mean value of $1.5 million and a standard deviation (s.d.) of $120,000.


    Calculate P (X < $1 million)
    Pr(Z < -4.1667).

    Your tables will give zero as the answer. Which is correct, to four decimal places.
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  3. #3
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    any chance of explaining it please
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  4. #4
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    so would it be 1M-1.5M/120,000 is that how you did it.
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    Quote Originally Posted by crashuk View Post
    so would it be 1M-1.5M/120,000 is that how you did it.
    That's how I got the z-value, yes.
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    Suppose a random sample of 10 firms gave a mean profit of $900,000 and a (sample) standard deviation of $100,000.

    so i do the same steps as the rest?
    so here i would use T as the random sample of 10 is under 30, 30 and over i use z system and for T 29 and less . is that correct?
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  7. #7
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    Quote Originally Posted by crashuk View Post
    Suppose a random sample of 10 firms gave a mean profit of $900,000 and a (sample) standard deviation of $100,000.

    so i do the same steps as the rest?
    This one will probably be different. What does the question ask you to do?
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  8. #8
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    Suppose a random sample of 10 firms gave a mean profit of $900,000 and a (sample) standard deviation of $100,000. Establish a 95% confidence interval for the true mean profit in the industry. Which probability distribution do you use? Why?
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  9. #9
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    Quote Originally Posted by crashuk View Post
    Suppose a random sample of 10 firms gave a mean profit of $900,000 and a (sample) standard deviation of $100,000. Establish a 95% confidence interval for the true mean profit in the industry. Which probability distribution do you use? Why?
    Use the t-distribution because the population sd is unknown. Although n is small (n < 30), from your previous question it's known that the data comes from a normal population so using the t-distribution is OK.

    As for the confidence interval, you will find the necessary formulae at this thread: http://www.mathhelpforum.com/math-he...intervals.html
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