Confidence interval and sample size
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1) Suppose that 64 smokers were sampled. Assume the sample mean and the sample standard deviation remained the same ($20 and $5, respectively).
a. What is the 95% confidence interval estimate of u?
b. A research a firm a conducted a survey to determine the mean amount of steady smokers spend on cigarettes during a week. A sample of 49 steady smokers revealed that X = $20 and s= $5. What is the 95% confidence interval estimate of u?
Explain why this confidence interval is narrower than the one determined in the previous exercise.
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Solution Summary
The confidence interval for different sample sizes have been calculated.
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1) Suppose that 64 smokers were sampled. Assume the sample mean and the sample standard deviation remained the same ($20 and $5, respectively).
a. What is the 95% confidence interval estimate of u?
Confidence limits
Mean=M = $20
Standard deviation =s= $5
sample size=n= 64
sx=standard error of mean=s/square root of n= 0.625 = ( 5 /square root of 64)
Confidence level= 95%
Therefore Significance level=alpha (a) = 5% =100% -95%
No of tails= 2
This is 2 tailed because we are calculating the 2 sided confidence interval for the average income
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