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Exam 9: Estimation and Confidence Intervals

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Question 61

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A sample mean is a _______________ estimate of the population mean.

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Question 62

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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. They sampled 240 students and found a mean of 22.3 hours per week. Assuming a population standard deviation of six hours, what is the 99% level of confidence?

A) [21.80, 22.80]
B) [16.3, 28.3]
C) [21.30, 23.30]
D) [20.22, 22.0]

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Question 63

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

If 95% and 98% confidence intervals were developed to estimate the true cost of an MP3 player with a known population standard deviation, what differences would they have?

A university wants to determine the proportion of students who use a cash card to pay at the university food service. Out of 100 students surveyed, 65 students use a cash card. What is the 95% confidence interval for the population proportion?

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 population mean. He selects and weighs a random sample of 49 trucks and finds the mean weight is 15.8 tons. The population standard deviation is 3.8 tons. What is the 95% confidence interval for the population mean?

The distribution of Student's t is ________.

A sample mean is the best point estimate of _______.

A company's headquarters is located in downtown Chicago. If they require their employees to start working at 6:00 a.m., the company is interested to know the mean driving time of its employees. Fifty employees are randomly sampled over four weeks and asked to record their driving times. The mean driving time is 35 minutes, with a standard deviation of 10 minutes. What is the 98% confidence interval for the population mean?

A(n) _________ estimate states the range within which a population parameter probably lies.

The probability that an interval estimate includes the population parameter is called the _____________.

We want to estimate the population mean of waiting time in a doctor's office within 20 minutes, with a 99% level of confidence. The population standard deviation is estimated to be 15. How large a sample is required?

A survey of 50 retail stores revealed that the average price of a microwave was $375, with a sample standard deviation of $20. If 90% and 95% confidence intervals were developed to estimate the true cost of the microwave, what similarities would they have?

The interval within which a population parameter is expected to lie is called a __________.

A university surveyed recent graduates of the English Department for their starting salaries. Four hundred graduates returned the survey. The average salary was $25,000, with a standard deviation of $2,500. What is the best point estimate of the population mean?

A university surveyed recent graduates of the English Department for their starting salaries. Four hundred graduates returned the survey. The average salary was $25,000. The population standard deviation is $2,500. A 95% confidence interval is constructed. What does the confidence interval mean?

A sample of 50 is selected from a known population of 250 elements. The population standard deviation is 15. Using the finite correction factor, what is the standard error of the sample means?

A research firm needs to estimate within 3% the proportion of junior executives leaving large manufacturing companies within three years. A 0.95 degree of confidence is to be used. Several years ago, a study revealed that 21% of junior executives left their company within three years. To update this study, how many junior executives should be surveyed?

There are 2,000 eligible voters in a precinct. A total of 500 voters are randomly selected and asked whether they plan to vote for the Democratic incumbent or the Republican challenger. Of the 500 surveyed, 350 said they would vote for the Democratic incumbent. Using the 0.99 confidence coefficient, what are the confidence limits for the proportion that plan to vote for the Democratic incumbent?

A finite population correction factor is used when we know the _________________.