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8. California Speeding. A simple random sample of 40 recorded speeds (in mph) is obtained from cars traveling on a section of Highway 405 in Los Angeles. The sample has a mean of 68.4 mph and a standard deviation of 5.7 mph. Use a 0.05 significance level to test the claim that the mean speed of all cars is greater than the posted speed limit of 65 mph. t=. X - M S In