Question

A tire manufacturer claims that the life span of its tires is 52,000 miles. Assume the life spans of the tire are normally distributed. You selected 16 tires at random and tested them. The mean life span of the sample is 50,802 miles. The tires had a population standard deviation, σ = 800. Use the .05 level of significance. a) Which distribution would be indicated? b) Explain why you chose that distribution. c) Construct a confidence interval for the mean using the above data. Use the .05 level of significance. d) Re-compute the confidence interval if “n” is increased to 125 with the same mean and standard deviation. e) Re-compute the confidence interval if level of significance .01 with the same mean and standard deviation with the original n.

Answer 1

Given,

a).

Normal distribution (z).

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b)

We are using normal distribution because population standard deviation is known.

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c)

95% confidence interval for is,

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d)

If n=125

95% confidence interval for is,

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e).

99% confidence interval for is,

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