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# hws62 - 7.12 a A 95 confidence interval for µ is σ 1000 x...

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°±²³² ´µ ¶·¸¹º»¼½¾»¿ÀÁ ±»Â·Ã¸»ÄÅ 7.12 a . A 95% confidence interval for μ is x ± n σ 96 . 1 196 600 , 32 100 1000 96 . 1 600 , 32 ± ° ± ° or \$32,404 < μ < \$32,796. b . A point estimate for the mean starting salary for Marketing/Sales is x =\$24,100 and the margin of error is x ± 8 . 156 100 800 96 . 1 96 . 1 = n σ c. A 98% confidence interval for μ is x ± n σ 33 . 2 4 . 186 909 , 24 100 800 33 . 2 909 , 22 ± ° ± ° or \$22,722.60 < μ < \$23,095.40 7.20. a. Indexing 05 . t with 9 1 = - n degrees of freedom in Table 4, we have 05 . t = 1.833. Hence the 90% confidence interval is x ± n s t 05 . 133 . 5 . 8 10 23 . 833 . 1 5 . 8 ± ° ± ° or 8.367 < μ < 8.633. b . The 90% confidence interval does not contain the mean 8.7% rate that prevails in the bank’s market area. Hence, we can conclude with a fair amount of certainty that the population from which we are sampling is not 8.7%. Perhaps the loan applicants at this particular bank do not represent a random sample of all applications in the market area. 7.23. a . Calculate 6 . 171 = ± i x and . 08 . 2699 2 = ± i x Then 6 . 15 11 6 . 171 = = = ± n x x i 212 . 2 10 11 ) 6 . 171 ( 08 . 2699 1 ) ( 2 2 2 2 = - = - - = ± ± n n x x s i i

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