A utility company sampled 484 customers, and finds that 132 of them had a discre

Question

A utility company sampled 484 customers, and finds that 132 of them had a discrepancy on their service bill. What is the upper bound for the 99% confidence interval for the proportion of customers with a discrepancy on their service bill? Round to three decimal places (for example: 0.419). Write only a number as your answer. A pollster wants to construct a 95% confidence interval for the proportion of adults who believe that economic conditions are getting better. A Gallup poll taken in July 2010 estimates this proportion to be 0.33. Using this estimate, what sample size is needed so that the confidence interval will have a margin of error of o.089? Write only an integer as your answer. A researcher wants to construct a 99% confidence interval for the proportion of people who changed jobs in the past year. what sample size is needed so that the confidence interval will have a margin of error of 0.019.

Explanation / Answer

18) here estimated proportion p=132/484=0.273

std error =(p(1-p)/n)1/2 =0.0202

for 99% CI, z=2.5758

therefore upper confidence interval =p+z*std errror =0.325

19)

p=0.33

margin of error E =0.089

for 95% CI, z=1.96

therefore sample size n=p(1-p)*(Z/E)2 =108

20)

here as estimated proportion not known p=0.5

for 99% CI, z=2.5758

sample size =p(1-p)*(Z/E)2 =4595

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