1) An artidle described an investigation into the coating weights for large pipe

Question

1) An artidle described an investigation into the coating weights for large pipes resulting Production standards call for a true average weight from a galvanized coating process of 200 lb per pipe. The accompanying descriptive summary and boxplot are from Minitab. 03 Variable N Mean Median TrMean StDev SEMean ctg wt 30 206.32 206.00 206.81 635 1.16 193.00 218.00 202.75 212.00 Min Max Coating weight 200 210 220 What does the boxplot suggest about the status of the specification for true average coating weight? Choose the correct statement! a) It appears that the true average weight is approximately 202 lb per pipe. It appears that the true average weight is approximately 218 lb per pipe. It appears that the true average weight could be significantly off fromn the production specification of 200 lb per pipe. It appears that the true average weight is not significantly different from the production specification of 200 lb per pipe. · . · .

Explanation / Answer

Question 1

Part a

Correct Answer:

It appears that the true average weight could be significantly off from the production specification of 200 lb per pipe.

Explanation: The median or mean of the given box plot is indicating that it is significantly greater than production specification of 200 lb per pipe.

Part b

We have to use one sample t test for population mean. Null and alternative hypothesis for this test is given as below:

H0: µ = 200 versus Ha: µ 200

This is a two tailed test.

We are given

= 0.05

n = 30

Xbar = 206.32

S = 6.35

df = n – 1 = 30 – 1 = 29

test statistic = t = (Xbar - µ) / [S/sqrt(n)]

t = (206.32 – 200) / [6.35/sqrt(30)]

t = 5.4513

P-value = 0.0000

(By using t-table or excel)

P-value < = 0.05

So, we reject the null hypothesis H0

There is sufficient evidence to conclude that average weight differs from 200 lb per pipe.

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