"A machine that produces metal rods used in an automobile suspension system is being tested to
make sure that the average diameter of rods it produces does not exceed 8.20mm. A random
sample of 15 rods is selected, and the diameter (in mm) is measured for each rod. The resulting
data are shown below."
8.24 8.23 8.20 8.21 8.20 8.28 8.23 8.26 8.24 8.25 8.19 8.25 8.26
8.23 8.24
You may use any statistical software to answer the following questions:
StatCrunch
A. Test of Significance
State:
Does the data provide sufficient evidence that the mean rod diameter exceeds 8.20 mm using a
0.05 level of significance? Please use the fourstep process.
Plan:
•
State the name of the appropriate test procedure (e.g. matched pairs t test) (1 pt)
The sample is randomly selected as a simple random sample. This is a onesample t test.
•
Describe the parameter being tested and the population of interest in the context of the
problem (2 pts)
The parameter being tested is the average diameter of rods that an automobile suspension
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 Spring '10
 BRUCEJAYCOLLINGS
 Statistics, Statistical hypothesis testing, Simple random sample

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