11. The market researcher’s boss would like a more precise (narrower) confidence
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Question
11. The market researcher’s boss would like a more precise (narrower) confidence interval than the one reported in Q 6. What are two things the market researcher might choose to do to make the confidence interval narrower? 12. Assume that SAT scores vary normally with a standard deviation of 100. How many students should be sampled if we want to estimate the population mean SAT at 90% confidence with a margin of error equal to 25? [Show your work.] 13. What is the critical t value for a 95% confidence interval using a sample size of 129? Use Excel instead of the table in your text to get a precise answer. 14. A stationery store wants to estimate the mean retail value of greeting cards that it has in its inventory. A random sample of 20 greeting cards indicates an average value of $1.67 and a sample standard deviation of $0.32. Set up a 95% confidence interval estimate of the mean value of all greeting cards in the store’s inventory. (Assume the population is normally distributed.) [HINT: Think about which confidence interval formula you want to use here.] [Show your work.]
Explanation / Answer
11. 1. Increase sample size
2. decrease critical value (Use 95% confidence Level vs 99% confidence level)
12.
14
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