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Math Help - Urgent HW Project Due tomorrow =(

  1. #1
    Newbie derek408's Avatar
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    Urgent HW Project Due tomorrow Confidence Interval Problem=(

    I'm stuck on this problem, i can't figure what the standard deviation is, and im not sure if 45 is the mean.


    1) A new public telephone has been installed at the airport baggage-claim area. A quarter was lost 45 of the 300 times that it was used. Find a 95% confidence interval for the true proportion of times that a user will lose a quarter.
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  2. #2
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    The proportion is approximatly normally distributed..
    The sample proportion is \bar{Y}=\frac{45}{300}=0.15=p

    So the 95% CI is given by
    \bar{Y} \pm z_{.05/2} \sqrt{\frac{p\cdot (1-p)}{n}}
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  3. #3
    Newbie derek408's Avatar
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    hey thanks rob youre the greatest ! rob is that the answer or a setup for the problem?

    would n=300?
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  4. #4
    Newbie derek408's Avatar
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    if the confidence level is 95%, then the z score would be 1.96?
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  5. #5
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    Thats the setup for the answer. Yeah, n is equal to 300, so just plug the numbers in to get the lower and upper confidence intervals. And z_{.05/2}=1.96
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  6. #6
    Newbie derek408's Avatar
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    thanks =)!
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