An automobile dealership offers to fill the four tires of your new car with 100% nitrogen for a cost of $20. The dealership claims that nitrogen-filled tires run cooler than those filled with compressed air, and they advertise that nitrogen extends tire mileage (life) by 25%. If new tires cost $50 each and are guaranteed to get 50,000 miles (filled with air) before they require replacement, is the dealership's offer a good deal?