Exam 8: Statistical Inference: Estimation for Single Populations

In estimating the sample size necessary to estimate a population mean, the error of estimation, E, is equal to the difference between the sample mean and the sample standard deviation.

James Desreumaux, VP of Human Resources of American First Banks (AFB), is reviewing the employee training programs of AFB.His staff randomly selected personnel files for 10 tellers in the southwest region, and determined that their mean training time was 25 hours and that the standard deviation was 5 hours.Assume that training times are normally distributed.The 90% confidence interval for the population variance of training times is ________.

Life tests performed on a sample of 13 batteries of a new model indicated: (1)an average life of 75 months, and (2)a standard deviation of 5 months.Other battery models, produced by similar processes, have normally distributed life spans.The 90% confidence interval for the population mean life of the new model is _________.

A researcher is interested in estimating the mean weight of a semi tractor truck to determine the potential load capacity.She takes a random sample of 17 trucks and computes a sample mean of 20,000 pounds with sample standard deviation of 1,500.The 90% confidence interval for the population mean weight of a semi tractor truck is ______________.

Suppose a random sample of 16 is selected from a population with a normal distribution with a known population standard deviation σ of 10.Assume that the sample mean is 4.2.Based on a 90% confidence interval for the population mean, we can conclude that 0.1 is a plausible number for the population mean μ.

The t score (or table value for Student's t distribution)associated with the upper 5% and 48 degrees of freedom is ______.

Given n = 17, s² = 18.56, and that the population is normally distributed, the 80% confidence interval for the population variance is ________.

A large trucking company wants to estimate the proportion of its tracker truck population with refrigerated carrier capacity.A random sample of 200 tracker trucks is taken and 30% of the sample have refrigerated carrier capacity.The 90% confidence interval to estimate the population proportion is _______.

A large trucking company wants to estimate the proportion of its tractor truck population with refrigerated carrier capacity.A random sample of 200 tractor trucks is taken and 30% of the sample have refrigerated carrier capacity.The 95% confidence interval to estimate the population proportion is _______.

A study is going to be conducted in which a population mean will be estimated using a 92% confidence interval.The estimate needs to be within 12 of the actual population mean.The population variance is estimated to be around 2500.The necessary sample size should be at least _______.

The z value associated with a two-sided 95% confidence interval is _______.

When a range of values is used to estimate a population parameter, it is called a range estimate.

Catherine Chao, Director of Marketing Research, is evaluating consumer acceptance of a new toothpaste package.She plans to use a 95% confidence interval estimate of the proportion of households which prefer the new packages; she will accept a 0.05 error.Previous studies indicate that new packaging has an approximately 70% acceptance rate.The sample size should be at least _______.

Suppose a researcher is interested in understanding the variation in the price of store brand milk.A random sample of 36 grocery stores is selected from a population and the mean price of store brand milk is calculated.The sample mean is $3.13 with a standard deviation of $0.23.Construct a 95% confidence interval to estimate the population mean.