Exam 9: Estimation and Confidence Intervals

In relative terms, a _______ standard deviation leads to a narrower confidence interval.

Deciding on the number of observations to include in a sample is an important decision when planning a research study. What information is required to make this decision?

Of the following characteristics, the t distribution and z distribution are the same in all BUT one. Which one is it?

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% confidence interval estimate of µ?

A random sample of 85 supervisors revealed that they worked an average of 6.5 years before being promoted. The population standard deviation was 1.7 years. Using the 0.95 degree of confidence, what is the confidence interval for the population mean?

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?

A bank wishes to estimate the mean credit card balance owed by its customers. The population standard deviation is estimated to be $300. If a 98% confidence interval is used and an interval of $75 is desired, how many customers should be sampled?

A sample of 2,000 union members was selected, and a survey recorded their opinions regarding a proposed management union contract. A total of 1,600 members were in favor of it. A 95% confidence interval estimated that the population proportion was between 0.78 and 0.82. This indicates that about 80 out of 100 similarly constructed intervals would include the population proportion.

The estimate of the population proportion is to be within plus or minus .10, with a 95% level of confidence. The best estimate of the population proportion is .25. How large a sample is required?

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. Estimate the value of the population proportion.

A sample standard deviation is the best point estimate of the ___________.

A population has a standard deviation of 25. We want to estimate the population mean within 2, with a 95% level of confidence. How large a sample is required?

A company wants to estimate next year's total revenue. Why is an interval estimate preferred to a point estimate?

When using the t distribution to calculate a confidence interval, we assume that the population of interest is normal or nearly normal.