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# problemset9solution - 1 PAM 210 Lecture 1 Problem Set#9...

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PAM 210 Lecture 1 Problem Set #9 Posted: 14 th April, 2008 Due date: 21 st April, 2008 #1) You will have complete sales information for last month in a week, but right now you have data from a random sample of 31 stores. The mean change in sales in the sample is x = 4.2 and the standard deviation of the changes in the sample is s = 10. Here are the null and alternative hypotheses: H 0 : μ = 0 H a : μ 0 a) Find the t-statistic. Round your answer to three decimal places, if necessary. Ans. The t-statistic is 338 . 2 31 / 10 0 2 . 4 - = t (10 points . Full credit for the correct answer. 8 points if the final answer was wrong but the formula was correct) b) Is the result statistically significant at the 1% level? Ans. The df =31-1=30. Since this is a two-sided test, the critical value is 75 . 2 ) 30 ( 005 . 0 = t . Since 2.338<2.75, the result is not significant at the 1% level. (10 points. Full credit if the final answer is correct (significant/not significant). If the final answer is wrong, then 5 points for correct df, and 3 more points for the correct critical value) #2) A bank wonders whether omitting the annual credit card fee for customers who charge at least three thousand dollars in a year would increase the amount charged on its credit card. The bank makes this offer to an SRS of 1001 of its existing credit card customers.

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problemset9solution - 1 PAM 210 Lecture 1 Problem Set#9...

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