1. A manufacturing company produces car tires that have a length of life that is approx., normally distributed with mean and standard deviation of 50 hr.'s. If a random sample of 15 tires has a mean of 780 hr.'s, construct a 90% confidence interval for the population mean. 2. The contents of 7 similar containers of carbon dioxide with mean 10 and standard deviation is 0.283 liters. Construct a 90% confidence interval for the Mean of all such containers assuming that contents are normally distributed. 3. A standard mathematics test was given to 60 girls and 80 boys. The girls made an average of 85 while the boys made an average of 76. Construct a 90% confidence interval of the difference between the population means assuming that both populations are normally distributed with variances 64 and 36 for boys and girls respectively.