hw_04 - Name(s) (up to four students per homework set):...

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Due: In class, Friday February 15, 2008 Name(s) (up to four students per homework set) : Section number(s) 1. 2. 3. 4. For instructor or TA use only: Problem Score Points 1 10 2 15 3 15 4 20 5 15 6 15 7 10 M E 345 Spring Semester, 2008 Homework Set # 4 Professor J. M. Cimbala Total: 100 1 . (10 pts) A large manufacturing plant uses a certain brand of light bulbs that has a mean time to failure (MTTF) of 3600 hours with a standard deviation of 160 hours. Good lighting in the plant is critical to safety, and the plant manager determines that no more than 10% of the bulbs should fail while being used. He institutes a policy to replace all the light bulbs simultaneously according to a set schedule, rather than to replace individual bulbs as they burn out. After how many hours should all the bulbs be replaced such that no more than 10% of the bulbs will fail while being used? (You may assume that the variations in MTTF are random .) 2 . (15 pts) A quality control engineer pulls 10 bearings at random from an assembly line, and measures the diameter of each one. The measurements are 5.08, 5.16, 5.06, 5.04, 5.10, 5.18, 5.04, 5.06, 5.12, and 5.09 mm. ( a ) Estimate the population mean and its confidence interval for 95% confidence level. For consistency, give your answer to three decimal places to the right of the decimal point. ( b ) Estimate the population standard deviation and its confidence interval for 95% confidence level. For consistency, give your answer to three decimal places to the right of the decimal point.
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This note was uploaded on 07/23/2008 for the course ME 345 taught by Professor Staff during the Spring '08 term at Pennsylvania State University, University Park.

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hw_04 - Name(s) (up to four students per homework set):...

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