# Hypothesis Testing on Maintenance Costs of Trucks

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An Electric Co. Operates a fleet of trucks that provide electrical service to the construction industry. Monthly mean maintenance cost has been $75 per truck. A random sample of 40 trucks provided a sample mean of $82.50 per month, with a sample deviation of $30. Managers want a test to determine whether the mean monthly maintence cost has increased.

A. Using a .05 level of significance, what is the rejection rule for this test?

B. what is your conclusion based on the sample mean of $82.50?

C. what is the p-value associated with the sample result? What is your conclusion based on the p-value?

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The solution answers the question(s) below.

###### Education

- BSc , Wuhan Univ. China
- MA, Shandong Univ.

###### Recent Feedback

- "Your solution, looks excellent. I recognize things from previous chapters. I have seen the standard deviation formula you used to get 5.154. I do understand the Central Limit Theorem needs the sample size (n) to be greater than 30, we have 100. I do understand the sample mean(s) of the population will follow a normal distribution, and that CLT states the sample mean of population is the population (mean), we have 143.74. But when and WHY do we use the standard deviation formula where you got 5.154. WHEN & Why use standard deviation of the sample mean. I don't understand, why don't we simply use the "100" I understand that standard deviation is the square root of variance. I do understand that the variance is the square of the differences of each sample data value minus the mean. But somehow, why not use 100, why use standard deviation of sample mean? Please help explain."
- "excellent work"
- "Thank you so much for all of your help!!! I will be posting another assignment. Please let me know (once posted), if the credits I'm offering is enough or you ! Thanks again!"
- "Thank you"
- "Thank you very much for your valuable time and assistance!"

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