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Stat 231 Final F11

# Stat 231 Final F11 - Stat 231 Final Exam Fall 2011 I have...

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1 Stat 231 Final Exam Fall 2011 I have neither given nor received unauthorized assistance on this exam. ________________________________________________________ Name Signed Date _________________________________________________________ Name Printed

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2 1. An experiment was run to compare the fracture toughness of high purity 18% Ni-maraging steel to that of commercial purity steel of the same type. Summary statistics for the measured toughness of several specimens of each type are below. (Units are MPa m .) High Purity Commercial Purity 1 10 specimens tested n = 2 8 specimens tested n = 1 65.6 x = 2 59.8 x = 1 .8 s = 2 1.1 s = a) Give a one-sided lower 95% confidence bound for the ratio of standard deviations of toughness for specimens of this type, 12 / σσ . (Plug in completely, but you need not simplify.) b) Because it is expensive, an engineer wants to specify High Purity steel for use in a project only if its mean fracture toughness exceeds that of Commercial Purity steel by more than 4 MPa m . With .10 α = do the data summarized above force the conclusion that High Purity steel should be specified? (Show the whole 7-step hypothesis testing format/process.) 10 pts 15 pts
3 c) Give 95% two-sided confidence limits for the difference in mean fracture toughness for specimens of these two types of steel (High Purity minus Commercial Purity). (Plug in completely, but you need not simplify.) d) Assuming that fracture toughness measurements of specimens of Commercial Purity steel are normally distributed, give two-sided limits that you are 95% sure contain 99% of such measurements. (Plug in completely, but you need not simplify.) 10 pts 10 pts

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4 2. Company officials at a meat processor are concerned with the fraction of packages of sausage filled by a particular machine that contain more than 16.1 oz of sausage. They plan to weigh the net contents of a sample of packages filled by the machine. a) If 15 packages are to be weighed and roughly 30% of all packages actually contain more than 16.1 oz of sausage, find the probability that 8 or more in the sample hold more than 16.1 oz of sausage.
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Stat 231 Final F11 - Stat 231 Final Exam Fall 2011 I have...

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