Armstead Tires produces tires with a useful life that follows a normal pattern. Average life is 36,000 miles, with a standard deviation of 1500 miles.
a. What percentage of the tires will have a useful life between 38,000 and 40,000 miles?
b. What percentage of the tires will have a useful life less than 35,000 miles?
c. What percentage of the tires will have a useful life more than 39,000 miles?
d. Suppose the company wants to establish a warranty policy. Any tire not lasting as long as the warranty mileage will be replaced free of charge. What warranty mileage would you suggest to ensure that the company won’t have to replace more that 3% of the tires sold?