In the June 1986 issue of Consumer Reports, some data on the calorie content of beef hot dogs is given. Here are the numbers of calories in 20 different hot dog brands: 186; 181; 176; 149; 184; 190; 158; 139; 175; 148; 152; 111; 141; 153; 190; 157; 131; 149; 135; 132: Assume that these numbers are the observed values from a random sample of twenty independent normal random variables with mean and variance 2, both unknown. Find a 90% confidence interval for the mean number of calories .