A new extended-life light bulb has an average service life of 768 hours, with a standard deviation of 45 hours. If the service life of these light bulbs approximates a normal distribution, about what percent of the distribution will be between 617 hours and 917 hours?
Suppose a tire manufacturer wants to set a mileage guarantee on its new XB 70 tire. Tests revealed that the tire's mileage is normally distributed with a mean of 48,747 miles and a standard deviation of 2,309 miles. The manufacturer wants to set the guaranteed mileage so that no more than 5 percent of the tires will have to be replaced. What guaranteed mileage should the manufacturer announce?