# Until this year, the mean braking distance of a Nikton automobil

**Tutor description**

Until this year, the mean braking distance of a Nikton automobile moving at 60 mi per hour was 175 ft. Nikton engineers have developed what they consider a better braking system. They test the new brake system on a random sample of 81 cars and determine the sample mean braking distance. The results are the following. Sample Size = 81 Sample Mean = 167 ft Sample Standard Deviation = 27 ft a. Compute the 95% confidence interval for the mean braking distance. b. Interpret this interval. c. How many cars should be tested if Nikton wants to be 95% confident of being within 2 ft of the population mean braking distance?

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