Finding a Confidence Interval (No Standard Deviation nor Mean given)

hustisyawright

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Feb 13, 2020
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Hello, I am having a hard time solving this problem: The interval (20.6, 26.2) is a 90% confidence interval. Construct a 95% confidence interval for the same data. Use n=30. Thank you.
 

Subhotosh Khan

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Hello, I am having a hard time solving this problem: The interval (20.6, 26.2) is a 90% confidence interval. Construct a 95% confidence interval for the same data. Use n=30. Thank you.
Are the data normally distributed?

From the data given to you:

Can you calculate the mean (assuming normal distribution)?
 

HallsofIvy

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Jan 27, 2012
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Since you are given "n= 30" it sounds like you have a binomial distribution with some probability "p". For such a distribution the mean is np= 30p and the standard deviation is \(\displaystyle \sqrt{np(1-p)}\). Knowing the "90% confidence interval" you should be able to calculate p and then the 95% confidence interval.
 
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