Exam 8: Interval Estimation

A budget airline wants to estimate what proportion of customers would pay $10 for in-flight wireless access.Given that the airline has no prior knowledge of the proportion,how many customers would it have to sample to ensure a margin of error of no more than 5% for a 95% confidence interval?

A machine that is programmed to package 1.20 pounds of cereal is being tested for its accuracy in a sample of 36 cereal boxes,the sample mean filling weight is calculated as 1.22 pounds.The population standard deviation is known to be 0,06 pounds.Which of the following conclusions is correct?

Newscasters wish to predict the outcome of the next presidential election with 99% confidence and a margin of error equal to 0.08.Find the appropriate sample size to accomplish this goal.

A recent survey of 1,014 American adults found that 46% view environmental conditions as either "excellent" or "good" (Gallup,March 4-7,2010).Construct a 95% confidence interval of the population proportion.

In an examination of purchasing patterns of shoppers,a sample of 16 shoppers revealed that they spent,on average,$54 per hour of shopping.Based on previous years,the population standard deviation is thought to be $21 per hour of shopping.Assuming that the amount spent per hour of shopping is normally distributed,find a 90% confidence interval for the mean amount.

A sample of the weights of 35 babies is taken from the local hospital maternity ward.The point estimate for the mean weight of the babies is 110.2 ounces with a sample standard deviation of 23.4 ounces.Construct a 90% confidence interval for the population mean baby weight at this hospital.Interpret this interval.

The personnel department of a large corporation wants to estimate the family dental expenses of its employees to determine the feasibility of providing a dental insurance plan.A random sample of six employees reveals the following family dental expenses: $180,$260,$60,$40,$100,and $80.It is known that dental expenses follow a normal distribution.Construct a 90% confidence interval for the average family dental expenses for all employees of this corporation.

The ages of MBA students at a university are normally distributed with a known population variance of 10.24.Suppose you are asked to construct a 95% confidence interval for the population mean age if the mean of a sample of 36 students is 26.5 years.If a 99% confidence interval is constructed instead of a 95% confidence interval for the population mean,then _______________________________________________.

Given a sample mean of 12.5-drawn from a normal population,a sample of size 25,and a sample variance of 2.4-find a 99% confidence interval for the population mean.

An employee of the Bureau of Transportation Statistics has been given the task of estimating the proportion of on-time arrivals of a budget airline.A prior study has estimated this on-time arrival rate as 78.5%.What is the minimum number of arrivals this employee must include in the sample to ensure that the margin of error for a 95% confidence interval is no more than 0.05?

The width of the confidence interval is _____ times the margin of error.

A Monster.com pool of 3,057 individuals asked,"What's the longest vacation you plan to take this summer?" The following relative frequency distribution summarizes the results. The 95% confidence interval for the proportion of people who plan a one-week vacation this summer is ______.

Newscasters wish to predict the outcome of the next presidential election with 95% confidence and a margin of error equal to 0.08.Find the appropriate sample size to accomplish this goal.

Which of the following is the necessary condition for creating confidence intervals for the population mean?

A sample of 2,007 American adults was asked how they viewed China,with 17% of respondents calling the country "unfriendly" and 6% of respondents indicating the country was "an enemy".Construct a 95% confidence interval of the proportion of American adults who viewed China as either "unfriendly" or "an enemy."

The t_df distribution consists of a family of distributions where the actual shape of each one depends on the degrees of freedom,df.For lower values of df,the t_df distribution is similar to the z distribution.

Confidence intervals of the population mean may be created for the cases when the population standard deviation is known or unknown.How are these two cases treated differently?

To construct a 95% confidence interval for µ,the sampling distribution of must be _______.

What is the minimum sample size required to estimate a population mean with 95% confidence when the desired margin of error is E = 1.5? The population standard deviation is known to be 10.75.

The daily revenue from the sale of fried dough at a local street vendor in Boston is known to be normally distributed with a known standard deviation of $120.The revenue on each of the last 25 days is noted,and the average is computed as $550.Construct a 95% confidence interval for the population mean of the sale of fried dough by this vendor.