The quality control manager of a tire company wishes to estimate the tensile strength of a standard size of rubber used to make a class of radial tires. a random sample of 49 pieces of rubber from different production batches is subjected to a stress test. the test measures the force needed to break the rubber in pounds. according to the sample results, the average pressure is 250 pounds and the standard deviation is 42 pounds. determine the 95% confidence interval.