MATH 1342 Name ___________________________
Elementary Statistical Methods
Lab 6 – Ch.10 – Hypothesis Testing One Sample
Critical Thinking; Communication Skills; Empirical/Quantitative Skills
Suppose you are the manager of Speedy Oil Change which claims that it will change the oil in customers’ cars in less than 30 minutes on average. Further suppose that several complaints have been filed from customers stating that their oil change took longer than 30 minutes. Upper-level management at Speedy Oil Change headquarters has requested that you investigate the complaints.
To begin your investigation, you randomly audit 36 oil changes performed by Speedy Oil Change and record the time each customer waited for the oil change. The number of minutes to complete each of the 36 oil changes is reported below.
42 29 19 11 10 27
41 27 22 26 28 32
17
13
15
31
25
17
35
37
31
33
22
25
18 24 28 21 40 19
33 30 14 23 22 10
(data from http://org.elon.edu/econ/sac/Descriptive.htm
)
In the questions below, you will test if the mean is significantly less than 30 minutes at a significance level of 0.01.
1.
Write the null and alternative hypothesis. Label each accordingly.
2.
Calculate the Test Statistic and the P-value. Label each accordingly.
3.
Would you reject the null hypothesis? JUSTIFY your answer using a complete sentence and proper grammar. Do NOT write a conclusion.
4. Based on your answer to #3, i s the company fulfilling its promise to “change the oil in customers’ cars in less than 30 minutes on average?” (yes or no)

Lab Ch.9-10 continued
Unfortunately, Speedy Oil Change continues to get customer complaints. As the manager, you feel that perhaps more analysis is needed. You know that you are likely to be asked “how much less than
30 minutes is ou r mean oil change?”
5. Construct a 98% confidence interval. Report this confidence interval rounded to 1 decimal place.
6. Using the interval you created in #5, state the point estimate and calculate the margin of error for the interval. (1 decimal place)
7.
Explain to your superiors how to interpret this interval.
8.
Using the confidence interval you created, calculate the range of values that answers the question
“How much less than 30 minutes is our mean oil change?” Fill in the blanks below. (1 decimal place)
Our mean oil change is _________ to _________ minutes less than 30 minutes.
9.
What other STATISTICAL factors might you need to consider in order to address the customer s’ complaints?