Exam 9: Estimation and Confidence Intervals

A survey of 25 grocery stores revealed that the average price of a gallon of milk was $2.98 with a standard error of $0.10. What is the 95% confidence interval to estimate the true cost of a gallon of milk?

A random sample of 42 college graduates revealed that they worked an average of 5.5 years on the job before being promoted. The sample standard deviation was 1.1 years. Using the 0.99 degree of confidence, what is the confidence interval for the population mean?

The Nile Superstore is conducting a survey of consumer preferences for a new wireless, e-book reader. A sample of 160 people reveals that 120 would buy the new reader. Estimate the value of the population proportion.

What kind of distribution is the t distribution?

The mean weight of trucks traveling on a particular section of I-475 is not known. A state highway inspector needs an estimate of the mean. He selects a random sample of 49 trucks passing the weighing station and finds the mean weight is 15.8 tons. The population standard deviation is 3.8 tons. What is the 95 percent interval for the population mean?

25 percent of tourists going to Atlantic City to gamble spend more than $500. The Atlantic City Chamber of Commerce wants to update this percentage. For the new study, the estimate should be within 1% of the population proportion with a 90 percent confidence level. What is the necessary sample size?

A local politician wants an estimate of the proportion of the population who support her fiscal policies. She wants the estimate to be within .06 of the true proportion. Assume a 95 percent level of confidence. The politician's advisors estimated the proportion supporting her fiscal policy to be .60. How large of a sample is required?

In order to construct the 99 percent confidence interval, how many standard errors of the mean from the hypothesized population mean must you go? __________

Thirty-six items are randomly selected from a population of 150 items. The sample mean is 25 and the sample standard deviation 3. What is the finite population correction factor?

Assuming a population standard deviation of 3 hours, what is the required sample size if the error should be less than ½ hour with a 99% level of confidence?

A research firm conducted a survey to determine the mean amount people spend at a popular coffee shop during a week. They found the amounts spent per week followed a normal distribution with a population standard deviation of $4. A sample of 49 customers revealed that the mean is $25. What is the 95 percent confidence interval estimate of µ?

A group of statistics students decided to conduct a survey at their university to find the average (mean) amount of time students spent studying per week. Assuming a population standard deviation of 3 hours, what is the required sample size if the error should be less than ½ hour with a 99% level of confidence?

A sample of 100 is selected from a known population of 350 elements. The population standard deviation is 15. Using the finite correction factor, what is the standard error of the sample means?

Explain the concept of a confidence interval when estimating a population mean.

A research firm conducted a survey to determine the mean amount people spend at a popular coffee shop during a week. They found the amounts spent per week followed a normal distribution with a population standard deviation of $4. A sample of 64 customers revealed that the mean is $25. What is the 99 percent confidence interval estimate of µ?

A survey of corporate executives is being planned to determine their mean amount of weekly work time. A pilot survey indicated that the mean work time per week is 50 hours, with a standard deviation of 10 hours. It is desired to estimate the mean weekly work time within 5 hours. The 95 percent level of confidence is to be used. How many executives should be surveyed?

A point estimate is a single value used to estimate a population parameter.

For a given confidence interval, what is the interpretation of a 96% confidence level?

A finite population correction factor is used to adjust the _________________.

Other things being equal, a smaller sample size would result in a wider confidence interval because the standard error of the mean is ______________.