The manufacturer of the X-15 steel-belted redial truck tire claims that the mean mileage the tire can be driven before the tread wears out is at least 60,000 miles. Crosset Truck Company bought a sample of 48 tires and found that the mean mileage for its trucks is 59,000 miles (i.e. less than the manufacturer’s claim) with a standard deviation of 5,000 miles. 1) Test the manufacturer’s claim at a significance level (α) equals 5%. 2) Would your answer in part (1) change if the probability of type I error equals zero? Justify your answer. 3) Would your answer in (1) change if the confidence level changes to be 99%. Justify your answer with proper test

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The manufacturer of the X-15 steel-belted redial truck tire claims that the mean mileage the tire can be driven before the tread wears out is at least 60,000 miles. Crosset Truck Company bought a sample of 48 tires and found that the mean mileage for its trucks is 59,000 miles (i.e. less than the manufacturer’s claim) with a standard deviation of 5,000 miles. 1) Test the manufacturer’s claim at a significance level (α) equals 5%. 2) Would your answer in part (1) change if the probability of type I error equals zero? Justify your answer. 3) Would your answer in (1) change if the confidence level changes to be 99%. Justify your answer with proper test. 4) Another engineer has argued that tiers are considered to be fully consumed after 120000 mileage, test this claim at significance level of 10%. 5) If the manager of a store is thinking about establishing a new billing system for the store's credit costumers. After a thorough financial analysis, she determines that the new system will be cost effective only if the mean monthly income is more than 170£. A random sample of 400 monthly accounts is drawn, for which the sample mean is 178£. The manager knows that the accounts are normally distributed with standard deviation of 65£. Can the manager conclude from this that the new system will be cost-effective at significance level (α) equals 5%.?
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