1211 Xr1211 Tire manufacturers are constantly researching wa

12.11. [Xr12-11] Tire manufacturers are constantly researching ways to produce tires that last longer. New innovations are tested by professional drivers on race-tracks. However, any promising inventions are also test-driven by ordinary drivers. The latter tests are closer to what the tire company’s customers will actually experience. To determine whether a new steel-belted radial tire lasts longer than the company’s current model, suppose two new-design tires were installed on the rear wheels of 20 randomly selected cars and two existing-design tires were installed on the rear wheels of another 20 cars. All drivers were told to drive in their usual way until the tires wore out. The number of miles driven by each driver was recorded. Can the company infer that the new tire will last longer, on average, than the existing tire?

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