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. nu, when using the t-distribution table in this scenario?