Exam 9: Estimation and Confidence Intervals

A survey of an urban university (population of 25,450) showed that 870 of 1100 students sampled supported a fee increase to fund improvements to the student recreation center. Using the 99% level of confidence, what is the confidence interval for the proportion of students supporting the fee increase?

A random sample of 20 items is selected from a population. To determine the appropriate critical t-value what number of degrees of freedom should be used?

The finite population correction factor is applied when the population size is known.

A student wanted to construct a 95% confidence interval for the average age of students in her statistics class. She randomly selected 9 students. Their average age was 19.1 years with a standard deviation of 1.5 years. What is the 95% confidence interval for the population mean?

To compute a confidence interval, a __________ is used when the population standard deviation is unknown.

A local health care company wants to estimate the mean weekly elder day care cost. A sample of 10 facilities shows a mean of $250 per week with a standard deviation of $25. What is the 90 percent confidence interval for the population mean?

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 $2,500. A 95% confidence interval is constructed. What does the confidence interval mean?

A silkscreen printing company purchases t-shirts. To ensure the quality of the shipment, 300 t-shirts are randomly selected. 15 are defective. What is the 95 percent confidence interval for the proportion defective?

The population variation as measured by the standard deviation has little or no effect in determining the size of a sample selected from the population.

A confidence interval for a population proportion is based on using the uniform distribution to approximate the binomial distribution.

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. What is the 95 percent confidence interval for the population proportion?

A 95% confidence interval infers that the population mean

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?

A survey of households in a small town showed of 1200 sampled households, that in 850 households at least one member attended a town meeting during the year. Using the 99% level of confidence, what is the confidence interval for the proportion of households represented at a town meeting?

A student wanted to construct a 95% confidence interval for the average age of students in her statistics class. She randomly selected 9 students. Their average age was 19.1 years with a standard deviation of 1.5 years. What is the 99% confidence interval for the population mean?

A confidence interval is narrower when the standard deviation __________________.

A sample standard deviation is the best point estimate of the

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 tenth of a percent)?

A random sample of 42 college graduates revealed that they worked an average of 5.5 years on the job before being promoted. The population 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 within 20, with a 99 percent level of confidence. The population standard deviation is estimated to be 15. How large a sample is required?