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Unformatted text preview: Homework 7 Confidence Intervals Problem Conversion Guide: Problem in 5th Edition Corresponding Problem Number in 4th Ed. 810 88 814 812 840 836 843 834 848 842 860 854 Question 1 810. Past experience has indicated that the breaking strength of yarn used in manufacturing drapery material is normally distributed and that = 2 psi. A random sample of nine specimens is tested, and the average breaking strength is found to be 98 psi. Find a 95% twosided confidence interval on the true mean breaking strength. 95% Twosided CI on the breaking strength of yarn: where f8e5 x = 98, = 2 , n=9 and z 0.025 = 1.96 3 . 99 7 . 96 9 / ) 2 ( 96 . 1 98 9 / ) 2 ( 96 . 1 98 / / 025 . 025 . +  +  n z x n z x Question 2 814. The life in hours of a 75watt light bulb is known to be normally distributed with = 25 hours. A random sample of 20 bulbs has a mean life of gG = 1014 hours....
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 Spring '09
 Zafarani
 Normal Distribution, Student's tdistribution, χ α, twosided confidence interval

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