Amanufacturer of tires claims that the mean lifetime of these tires is as least 2000 miles when the production process is working properly. based upon past experiences, the standard deviation of the lifetime of the tires is 300 miles. the production manager will stop the production if there is evidence that the mean lifetime of the tires is below 2000 miles. if the production manager wishes to have 80% power of detecting a shift in the lifetime mean of the tires from 25000 to 24000 miles and if he is willing to take a 5% risk of committing a type i error, what sample size must be selected?