SOLUTION: A quality control engineer is interested in the mean length of sheet insulation being cut automatically by machine. The desired length of insulation is 12 metres. It is known that

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Question 254101: A quality control engineer is interested in the mean length of sheet insulation being cut automatically by machine. The desired length of insulation is 12 metres. It is known that the standard deviation in the cutting length is 0.15 metres. A sample of 144 cut sheets yield a mean length of 12.14 metres. This sample will be used to obtain a 90% confidence interval for the mean length cut by machine.
What are the two limits of the confidence interval? Min and max?
Answer by stanbon(75887) (Show Source):
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A quality control engineer is interested in the mean length of sheet insulation being cut automatically by machine.
The desired length of insulation is 12 metres. It is known that the standard deviation in the cutting length is 0.15 metres.
A sample of 144 cut sheets yield a mean length of 12.14 metres.
This sample will be used to obtain a 90% confidence interval for the mean length cut by machine.
What are the two limits of the confidence interval? Min and max?
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sample mean: 12.14 m
standard error: (invT(0.05,143)[0.15/sqrt(144)]
= 1.6556[0.15/12] = 0.0207
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Lower limit of 90% CI: 12.14-0.0207 =
Upper limit of 90% CI: 12.14+0.0207 =
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Cheers,
Stan H.