Exam 8: Interval Estimation

A random sample of 121 checking accounts at a bank showed an average daily balance of $280.The standard deviation of the population is known to be $66. a. Is it necessary to know anything about the shape of the distribution of the account balances in order to make an interval estimate of the mean of all the account balances? Explain. b. Find the standard error of the mean. c. Give a point estimate of the population mean. d. Construct an 80% confidence interval for the population mean. e. Construct a 95% confidence interval for the population mean.

The sample size needed to provide a margin of error of 3 or less with a .95 probability when the population standard deviation equals 11 is

Using an α = .04, a confidence interval for a population proportion is determined to be .65 to .75.For the same data, if α is decreased, the confidence interval for the population proportion

The t distribution should be used whenever the

Six hundred consumers belonging to the 25-34 age group were randomly selected in a city and were asked whether they would like to purchase a domestic or a foreign automobile.Their responses are given below. ​ Develop a 95% confidence interval for the proportion of all such consumers who prefer to purchase domestic automobiles.

In order to estimate the average time spent per student on the computer terminals at a local university, data were collected for a sample of 64 business students over a one-week period.Assume the population standard deviation is 1.6 hours.If the sample mean is 9 hours, then the 95% confidence interval is _____ hours.

If we want to provide a 95% confidence interval for the mean of a population, the confidence coefficient will be

When constructing a confidence interval for the population mean using the standard deviation of the sample, the degrees of freedom for the t distribution equals

A random sample of 64 SAT scores of students applying for merit scholarships showed an average of 1400 with a standard deviation of 240.The 95% confidence interval for the population mean SAT score is

A sample of 100 information systems managers had an average hourly income of $40.00 with a standard deviation of $8.00.The 95% confidence interval for the average hourly wage (in $) of all information system managers is

A random sample of 81 children with working mothers showed that they were absent from school an average of 6 days per term with a standard deviation of 1.8 days.Provide a 95% confidence interval for the average number of days absent per term for all the children in the school.

A random sample of 64 observations has a mean of 20, a median of 21, and a mode of 22.The population standard deviation is known to equal 4.8.The 95.44% confidence interval for the population mean is

The z value for a 97.8% confidence interval estimation is

The level of significance α

The use of the normal probability distribution as an approximation of the sampling distribution of is based on the condition that both np and n(1 - p) equal or exceed​

A random sample of 100 credit sales in a department store showed an average sale of $120.00.From past data, it is known that the standard deviation of the population is $40.00. a. Determine the standard error of the mean. b. With a .95 probability, determine the margin of error. c. What is the 95% confidence interval of the population mean?

In a sample of 400 voters, 360 indicated they favor the incumbent governor.The 95% confidence interval of voters not favoring the incumbent is

A statistician employed by a consumer testing organization reports that, at 95% confidence, he has determined that the true average content of the Uncola soft drinks is between 11.7 to 12.3 ounces.He further reports that his sample revealed an average content of 12 ounces, but he forgot to report the size of the sample he had selected.Assuming the standard deviation of the population is 1.28, determine the size of the sample.

It is known that the population variance equals 529.With a .95 probability, the sample size that needs to be taken if the desired margin of error is 4 or less is

As the degrees of freedom increase, the t distribution approaches the _____ distribution.