An article described an investigation into the coating weigh

An article described an investigation into the coating weights for large pipes resulting from a galvanized coating process. Production standards call for a true average weight of 200 lb per pipe. The accompanying descriptive summary and boxplot are from Minitab. What does the boxplot suggest about the status of the specification for true average coating weight? It appears that the true average weight could be significantly off from the production specification of 200 lb per pipe. It appears that the true average weight is approximately 218 lb per pipe. It appears that the true average weight is not significantly different from the production specification of 200 lb per pipe. It appears that the true average weight is approximately 202 lb per pipe. (b) A normal probability plot of the data was quite straight. Use the descriptive output to test the appropriate hypotheses. (Use a = 0.05.) State the appropriate hypotheses. Calculate the test statistic and determine the P-value. (Ro

Solution

a)

As we can see, the middle 50% of data (box part) is greater than 200.

Thus,

OPTION A: It appears that the true average weight could be significantly off from the production specification of 200 lb per pipe. [ANSWER]

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b)

Ho: u= 200
Ha: u > 200 [ANSWER]

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As we can see, this is a    right   tailed test.      
              
              
Getting the test statistic, as              
              
X = sample mean =    206.38          
uo = hypothesized mean =    200          
n = sample size =    30          
s = standard deviation =    6.35          
              
Thus, t = (X - uo) * sqrt(n) / s =    5.503102231 [ANSWER]          

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Also, the p value is              
              
p =    3.13638*10^-6       [ANSWER]

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As P < 0.05, we   REJECT THE NULL HYPOTHESIS.      

Thus, OPTION B: REJECT THE NULL HYPOTHESIS. There is sufficient evidence... [ANSWER, B]