Exam 9: Estimation and Confidence Intervals

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?

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 local retail company wants to estimate the mean amount spent by customers. Their store's budget limits the number of surveys to 225. What is their maximum error of the estimated mean amount spent for a 99% level of confidence and an estimated standard deviation of $10.00?

Suppose 1,600 of 2,000 registered voters sampled said they planned to vote for the Republican candidate for president. Using the 0.95 degree of confidence, what is the interval estimate for the population proportion (to the nearest 10^th of a percent)?

Sugar is packaged in 16-ounce bags. If 42 bags are sampled, with a mean of 15.95 ounces and a standard deviation of 0.4 ounces, what is the 99% confidence interval estimate of the population mean?

Approximately 25% 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% confidence level. What is the necessary sample size?

When deciding on the number of observations to include in a sample, what would favor larger sample sizes?

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.

To calculate the sample size required to estimate a population mean, we must know or estimate the ______________ of the population distribution.

What is the interpretation of a 96% confidence level?

One factor in determining the size of a sample is the degree of confidence selected. This is usually 0.95 or 0.99, but it may be any degree of confidence you specify.

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?

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

When using Student's t to compute an interval estimate, ___________.

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?

For a distribution of sample means with a known population standard deviation, about _____ percent of the sample means are within three standard errors of population mean.

The distribution of Student's t is ________.

When we use a confidence interval to reach a conclusion about the population mean, we are applying a type of reasoning or logic called __________.

A student wanted to construct a 95% confidence interval for the mean age of students in her statistics class. She randomly selected nine students. Their average age was 19.1 years with a sample standard deviation of 1.5 years. What is the best point estimate for the population mean?

A consultant is planning a survey of corporate executives 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. The consultant wants to estimate the mean weekly work time within five hours. The 95% level of confidence is to be used. How many executives should be surveyed?