The manager of a fleet of automobiles is testing two brands of radial tires and assigns one tire of each brand at random to the two rear wheels of eight cars and runs the cars until the tires wear out. The data (in kilometers) follow. Find a 99% confidence interval on the difference in mean life. Which brand would you prefer based on this calculation?

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Car Brand 1 Brand 2 34,318 1 36,925 45,300 36,240 2 42,280 35,500 32,100 37,210 48,360 31,950 38,015 47,800 37,810 33,215 6. 38,200 8. 33,500