6.1 solutions

# Need a 95 confidence interval for the mean sales 1075

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Need a 95% confidence interval for the mean sales 107.5 = \$107.5 \$5.68 million = between \$101.82 and \$113.18 million b. The average sales for the entire company last year was reported to be \$100 million. Do your data provide sufficient evidence that the average sales for the company is higher this year than last year? Use your answer to part a to decide Since all the likely values for average sales this year fall above 100, you can conclude that the average sales is higher this year than last year. 5. Scores on an MBA placement exam are reported to have a normal distribution with standard deviation 18. The exam officials stated that the average score for all students was 70, but you believe after taking this exam that the average must be lower than 70. You take a random sample of 50 students and find their average score is 67. a. Use your data to find a 95% confidence interval for the mean score for all students taking the MBA placement exam. Average exam score is 67 = (62.01 to 71.99) with 95% confidence b. Does your answer to part a support your theory that the average score for everyone taking the exam was less than 70? Discuss. Since 70 is one of the likely values for the average score, you can’t say the average has changed; your claim is not valid. 6. Which problems on this worksheet need the central limit theorem to solve, and which ones did not? Explain. Problems 2 and 5 already had a normal distribution so CLT was not needed. All other problems required the CLT (and hence a large sample size) to solve 3
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