Quiz 7 Solutions

Quiz 7 Solutions - BA 240 Spring 2008 W. Li 05/28/2008 QUIZ...

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BA 240 Spring 2008 W. Li 05/28/2008 QUIZ 7 Solution Account # 1 2 3 4 5 6 7 8 9 10 Year 2000 27 19 40 30 33 25 31 29 15 21 Year 1999 35 24 47 28 41 33 35 51 18 28 Difference -8 -5 -7 2 -8 -8 -4 -22 -3 -7 Summary Statistics for Difference: 7 d 128 . 6 d s 27 1 x 318 . 7 1 s 34 2 x 209 . 10 2 s a) Find a 95% confidence interval for the difference between the mean difference in the average account ages between 2000 and 1999. Interpret the result. (5 points) α = .05, α/2 = .025, df = 9 t .025, 9 = 2.262 6164 . 2 , 3826 . 11 3836 . 4 7 10 128 . 6 262 . 2 7 2 / n s t d d We are 95% confident that the average account ages in 2000 reduced from 2.6164 to 11.3826 days than the average account ages in 1999. b) Could the company claim that the mean average account age has been reduced by the company’s new policies? State null and alternative hypotheses, calculate the test statistics, find p -value, make your decision by comparing
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