each model. The population variances for the two models are unknown, but assumed to be not equal. Both population lifespans are assumed to be normally distributed. The sample mean difference is used to produce a confidence interval for the true mean difference in light bulb lifespan. QUESTION 5 The pollutant concentration in an airplane is assumed to be normally distributed. The sample mean for 17 sample air measurements is used to produce a 95% confidence interval for the true average pollutant concentration using the tablutate t-Distribution in Table A.4 (thus, the sample variance for the 17 sample measurements is used to approximate the population variance). What is the value for the degrees of freedom, i.e. , when using the t-Distribution table in this scenario? QUESTION 6 The pollutant concentration in an airplane is assumed to be normally distributed. The sample mean for 17 sample air measurements is used to produce a 95% confidence interval for the true average pollutant concentration using the tablutate t-Distribution in Table A.4 (thus, the sample variance for the 17 sample measurements is used to approximate the population variance). What is the t-statistic value read from the t-Distribution table in order to produce the 95% confidence interval? QUESTION 7 Which of the following combination of confidence level and sample size will produce the most precise (i.e. the narrowest) confidence interval for population mean or variance? 85% confidence level using a sample size of 40 85% confidence level using a sample size of 160 95% confidence level using a sample size of 40 O 95% confidence level using a sample size of 160