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Quiz 5 S2008 key

# Quiz 5 S2008 key - Quiz 5 Friday EMA 4714 Materials...

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Quiz 5 EMA 4714 - Materials Selection and Failure Analysis Friday, March 28, 2008 Name ________________________________________ Open Book/Open Notes 1. [10 points] Two batches [10,000 pieces each] of self-tapping steel fasteners were received from a heat treating facility who claimed that one batch had been tempered for twice the time as the other. The paperwork had been misplaced and there was no way of knowing which batch was which. A series of hardness measurements performed on pieces selected at random from each batch resulted in data contained within the table below. For your convenience, I have calculated means and standard deviations for the two sets of sample data. Based on your statistical analysis, and using a level of significance [ α ] of 0.05, does the data allow a determination that the two batches were subjected to different tempering times? Please show work! Batch 1 Batch 2 51 47 50 44 52 45 52 39 48 46 52 44 48 41 47 42 49 47 51 49 Mean = 50.0 Mean = 44.4 s 1 = 1.89 s 2 = 3.06 s 2 2 /s 1 = 9.378/3.556 = 2.638, less than F(table) = 3.180 Use Statistical Test 6, s unknown and s 1 = s 2 s p2 = [(n 1 -1)s 12 + (n 2 -1)s 22 ]/[n

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Quiz 5 S2008 key - Quiz 5 Friday EMA 4714 Materials...

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