Exam 8: Estimation and Confidence Intervals

The proportion of junior executives leaving large manufacturing companies within three years is to be estimated within 3 percent. The 0.95 degree of confidence is to be used. A study conducted several years ago revealed that the percent of junior executives leaving within three years was 21. To update this study, the files of how many junior executives should be studied?

The t distribution approaches as the sample size increases. As the sample size increases, the computed value of t .

The Sugar Producers Association wants to estimate the mean yearly sugar consumption. A sample of 16 people reveals the mean yearly consumption to be 27 kg with a sample standard deviation of 9 kg. Assume a normal population. Develop a 99% confidence interval for the mean annual consumption of sugar.

A survey of an urban university (population of 25,450) showed that 870 of 1,100 students sampled supported a fee increase to fund improvements to the student recreation center. If university officials say that at least 70% of the voting student population support the fee increase, what conclusion can be drawn based on a 95% level of confidence?

The mean number of travel days per year for the outside salespeople employed by hardware distributors is to be estimated. The 0.90 degree of confidence is to be used. The mean of a small pilot study was 150 days, with a standard deviation of 14 days. If the population mean is to be estimated within two days, how many outside salespeople should be sampled?

The Dean of the Business School wants to estimate the mean number of hours worked per week by students. A sample of only 12 students showed a mean of 24 hours with a standard deviation of 4 hours. Find the 95 percent confidence interval for the population mean.

Dr. Patton is a professor of English. Recently she counted the number of misspelled works in a group of student essays. She noted the distribution of misspelled words per essay followed the normal distribution with a standard deviation of 2.44 words per essay. For her Tuesday class of 44 students, the mean number of misspelled words per essay was 6.05. Construct a 90% confidence interval for the mean number of misspelled words in the population of student essays.

In order to construct a 90% confidence interval for the population mean when the population standard deviation is unknown and the sample size is 18, you should use the t-value indicated as:

The following summarizes the average price of Air Canada stock at the end of 20 randomly selected weeks in 2000. Determine a 95% confidence interval for the average Air Canada stock price in 2000.

A survey of 144 retail stores revealed that the average price of a DVD was $375 with a standard error of $20. If 90% and 95% confidence intervals were developed to estimate the true cost of the DVD, what similarities would they have?

In order to construct a 95% confidence interval for the population mean when the population standard deviation is unknown and the sample size is 15, you should use the t-value indicated as:

i. The t distribution is based on the assumption that the population of interest is normal or nearly normal. Ii) The t distribution is a continuous distribution. Iii) There is not one t distribution, but rather a "family" of t distributions.

A sample of 25 is selected from a known population of 100 elements. What is the finite population correction factor?

Which of the following is NOT necessary to determine how large a sample to select from a population?

The Sugar Producers Association wants to estimate the mean yearly sugar consumption. A sample of 25 people reveals the mean yearly consumption to be 27 kg with a sample standard deviation of 9 kg. Assume a normal population. For a 99% confidence interval, what is the critical value needed?

The following summarizes the amount of snowfall in Ontario over the past number of years. If 90% and 95% confidence intervals were developed to estimate the true average annual snowfall, what similarities would they have?

Recently, 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 known to be $2,500. What is the 95% confidence interval for the mean salary of all graduates from the English Department?

i. The Student t distribution has a greater spread than does the z distribution. As a result, the critical values of t for a given level of significance are larger in magnitude than the corresponding z critical values. Ii) The test statistic t has n-1 degrees of freedom. Iii) William S. Gosset, a brewmaster, developed the t test for the Guinness Brewery in Ireland, who published it in 1908 using the pen name "Student."

i. The test statistic for a problem involving a small sample of fewer than 30 and an unknown population standard deviation is the Student's t distribution. Ii) The t distribution approaches the Z distribution as the sample size increases. iii. As the sample size increases, the computed value of t decreases

Student's t is used when