Exam 8: Estimation of the Mean and Proportion

Each employee of a large company is encouraged to contribute,through payroll deduction,to an international charity.Annual contributions per employee follow (approximately)a normal distribution.You take a random sample of 25 employees and find that the sample mean annual contribution per employee is $501 with a standard deviation of $17.00.What are the boundaries for a 99% confidence interval for the population mean,rounded to two decimal places?

A random sample of 1,100 adults showed that 32% of them are smokers.Based on this sample,the 90% confidence interval for the proportion of all adults who are smokers,rounded to four decimal places,is:

We use the t distribution to make a confidence interval for the population mean if the population from which the sample is drawn is (approximately)normally distributed,the population standard deviation is unknown,and the sample size is at least:

We are using the mean of a sample as a point estimate for the mean of a normal distribution with a standard deviation of 5.The margin of error,with 95% confidence,for this estimate is 0.860.What is the sample size?

A researcher wants to estimate the mean age of all Business Week readers at a 99% confidence level.She wants the margin of error to be within 3.1 years of the population mean.The standard deviation of ages of all Business Week readers is 10.04 years.The sample size that will yield a margin of error within 3.1 of the population mean is:

The values assigned to a population parameter based on the value(s)of a sample statistic are:

Which of the following is not part of the procedure for estimating the value of a population parameter?

A t distribution has a standard deviation of .If the standard deviation is equal to 1.1055,what is the value of the t critical value for a 90% confidence interval?

Out of a sample of 639 gasoline purchases at a self-service gas station,544 were made with a credit or debit card.Obtain the predeterminated margin of error.Round your answer to three decimal places.

A random sample of 450 produced a sample proportion of 0.71.The 95% confidence interval for the population proportion,rounded to four decimal places,is:

The single value of a sample statistic that we assign to the population parameter is a:

A sample of size 65 from a population having standard deviation = 55 produced a mean of 234.00.The 95% confidence interval for the population mean (rounded to two decimal places)is:

A company wants to estimate,at a 95% confidence level,the proportion of all families who own its product.The most conservative estimate of the sample size that would limit the margin of error to be within 0.046 of the population proportion is:

A random sample of 354 persons showed that 306 do not have health insurance.Calculate the point estimate of the population proportion of persons who do not have health insurance.Round to 4 decimal places.

A scientist is estimating the mean lifetime of a newly-discovered insect.From a sample of 88 insects,she finds a sample mean of 49.2 days.Suppose that the population standard deviation of all lifetimes is 2.500 days.What are the boundaries for a 90% confidence interval for the mean lifetime of the insect,rounded to two decimal places?

The sample statistic used to estimate a population parameter is a(n):

When making a confidence interval for the population mean using the t procedures,the degrees of freedom for the t distribution are:

The mean IQ score of a sample of 61 students selected from a high school is 87.Suppose the standard deviation of IQ's at this school is = 8.4.The 99% confidence interval for the population mean (rounded to two decimal places)is:

A random sample of 188 produced a sample proportion of 0.40.The 98% confidence interval for the population proportion,rounded to four decimal places,is:

The width of a confidence interval depends on the size of the: