Exam 8: Estimation of the Mean and Proportion

An advisor to the mayor of a large city wants to estimate,within 2.450 minutes,the mean travel time to work for all employees who work within the city limits.He knows that the standard deviation of all travel times is 11.35 minutes.He also wants to achieve a 95% confidence interval.He will poll a random sample of city employees.How many employees should he poll?

A researcher wants to make a 95% confidence interval for a population mean.She wants the margin of error to be within 1.9 of the population mean.The population standard deviation is 11.07.The sample size that will yield a margin of error within 1.9 of the population mean is:

A sample of 20 elements produced a mean of 91.4 and a standard deviation of 11.16.Assuming that the population has a normal distribution,the 90% confidence interval for the population mean is:

The z value for a 85% confidence interval for the population mean with known is:

A sample of size 97 from a population having standard deviation = 7 produced a mean of 47.The 99% confidence interval for the population mean (rounded to two decimal places)is:

The margin of error for the population mean,assuming is known,is:

The value of t for 19 degrees of freedom and a 90% confidence interval is:

Which of the following conditions is required to use the t distribution to make a confidence interval for the population mean?

You can decrease the width of a confidence interval by:

The mean federal income tax paid last year by a random sample of 45 persons selected from a city was $4,242.Suppose the standard deviation of tax paid in this city is = $991.The 95% confidence interval for the population mean (rounded to two decimal places)is:

You are estimating the mean waiting time in line at a particular fast-food restaurant.You ask 30 customers,at varying times of the day,how long they waited in line before placing their order.You then take the average of these values and use this average to estimate the mean waiting time for all customers.The average of the 30 values is an example of a(n):

Which of the following is not an acceptable condition for using the t distribution to make a confidence interval for ?

Estimation is a procedure by which we assign a numerical value or numerical values to the:

A random sample of 8 houses selected from a city showed that the mean size of these houses is 1,881.0 square feet with a standard deviation of 328.00 square feet.Assuming that the sizes of all houses in this city have an approximate normal distribution,the 90% confidence interval for the mean size of all houses in this city,rounded to two decimal places,is:

A random sample of 12 life insurance policy holders showed that the mean value of their life insurance policies is $210,000 with a standard deviation of $44,600.Assuming that the values of life insurance policies for all such policy holders are approximately normally distributed,the 99% confidence interval for the mean value of all life insurance policies,rounded to two decimal places,is:

The confidence level of an interval estimate is denoted by:

The Eks Survey Company employs 2000 people to conduct telephone surveys.Because many people don't like to answer such surveys,many "hang-ups" (whereby the person hangs up without completing the survey)occur.The owner of Eks wants to determine the mean number of "hang-ups" per employee on a particular day,using 95% confidence.He samples 50 employees,and finds that the mean number of "hang-ups" on that day was 41.0.Suppose that the standard deviation of the number of "hang-ups" for all employees is 21.8 What is the value of the margin of error? (round to four decimal places)

A random sample of 82 customers,who visited a department store,spent an average of $71 at this store.Suppose the standard deviation of expenditures at this store is = $19.The 98% confidence interval for the population mean (rounded to two decimal places)is:

A sample of 25 elements produced a mean of 123.4 and a standard deviation of 18.32.Assuming that the population has a normal distribution,the 90% confidence interval for the population mean,rounded to two decimal places,is:

A researcher wants to make a 99% confidence interval for a population proportion.The most conservative estimate of the sample size that would limit the margin of error to be within 0.033 of the population proportion is: